Wide field scanning laser obstacle awareness system

ABSTRACT

A wide field scanning laser obstacle awareness system (LOAS) comprises: a plurality of first optical elements configured to direct a portion of a pulsed laser beam generated by a light source to a light detector, and to direct the pulsed laser beam to a beam expander wherein the pulsed laser beam is expanded; and at least one rotationally operated second optical element for directing the expanded pulsed laser beam from the system with a predetermined pattern scanned azimuthally over a wide field, the at least one rotationally operated second optical element also for receiving reflections of the pulsed laser beam from at least one object along the predetermined pattern and directing them to the laser beam expander wherein the laser beam reflections are focused; the plurality of first optical elements also configured to direct the focused laser beam reflections to the light detector for use in determining the location of the at least one object.

CROSS REFERENCE TO RELATED APPLICATIONS

The following patent applications include a specification and drawingscommon to the instant application:

U.S. patent application Ser. No. 09/946,057; entitled “Combined LOAS andLIDAR System”; and

U.S. patent application Ser. No. 09/946,048; entitled “System and MethodOf Measuring Flow Velocity In Three Axes”,

both of which being filed on even date with and assigned to the sameassignee as the instant application

BACKGROUND OF THE INVENTION

The present invention is directed to obstacle awareness systems, ingeneral, and more particularly to a wide field scanning obstacleawareness system.

A common flight hazard of any aircraft operating near the Earth is thepotential for collision with ground structures and obstacles.Helicopters, in particular, and now new classes of aircraft known asunmanned air vehicles (UAVs), often operate less than five hundred feetabove ground level (AGL). In this environment, it is not uncommon forthese aircraft to collide with electrical power lines, support wires forradio towers, or various structures and obstacles. These collisionstypically result in loss of life, significant aircraft damage, damage tothe structures or obstacles themselves, subsequent loss of powerdistribution on the electrical grid, and danger to persons and propertyon the ground. Aircraft, such as helicopters and UAVs, for example,typically operate in these low altitudes for take-off and landing,various low-level military maneuvers, and commercial applications, suchas electrical utility inspection or emergency rescue missions.

Inspecting electrical power lines from an aircraft requires flying closeto the Earth along high tension power lines and support structureslooking for damaged equipment. Use of helicopters permit electricutility inspection crews to cover a large area of the power grids over ashort period of time. Other helicopter applications which require lowflying flight profiles include emergency and rescue missions, medicalemergencies, border surveillance, and supply of floating oil platforms,for example. Likewise, UAV applications require autonomous control forsurveillance, take-off, landing and delivery of munitions. In all ofthese applications, the flight crew and aircraft are at risk ofcolliding with obstacles like power lines, cables, towers, and othersimilar support structures. The risk becomes even greater with poorvisibility and flights over unknown terrain. Depending on the type ofaircraft canopy, the lighting, and the environmental conditions, manyobstacles may become effectively invisible to the pilot and crew due tobackground clutter even under daylight conditions. Also, because of thenarrow field of view offered the pilot by the aircraft, some obstaclesmay not be seen until it is too late for avoidance. Surprisingly, thehighest accident rates are typically associated with clear conditionswhich indicates that during reduced states of pilot situationalawareness, identification of hazardous ground obstacles may occur lessregularly.

Some helicopters are equipped with structural wire strike protectionkits which are fitted on the front end of the aircraft and intended toforce a wire in the path of the aircraft to slide over the top or underthe bottom of the aircraft. However, for this device to be effective, acontacted wire must slide across the canopy and into the wire cutters.When this occurs, the wire is likely to be severed by the wirecutter(provided it meets certain size and strength envelopes), freeingthe aircraft from the hazards. It is not uncommon for electrical utilitycompanies to identify cut wires but have no report of a wire strikeaccident. In some cases this indicates the flight crew did not know theyhit a wire, much less cut it, or are reluctant to report the incident.However, if the wire does not slide across the canopy, and impacts otherareas of the helicopter such as the rotors or landing skids, the wirecannot be severed by the wire strike protection system. As tensionbuilds in the wire due to the forward motion, damage to the aircraftensues with penetration into the canopy and flight crew, damage to themain rotor resulting in an imbalance, or loss of tail rotor control. Inall these cases, the flight crew is in immediate life threateningdanger. Depending upon the degree of interaction, fatalities can beattributed to the high-g accelerations of the rotor imbalance, bluntforce trauma due to subsequent impact with the ground/aircraft, orharmful interactions with the wire resulting in significant lacerationsor electrocution. Accordingly, due to the many low-level flyingapplications and the increasing risks posed thereby, obstacle avoidancewarning systems for these aircraft have become of paramount importancefor the safety of the pilot and crew of the aircraft. These devices areintended to warn the flight crew in advance of the collision with theobstacle, so that they(or an automated flight control system)can takeevasive action prior to collision.

Amphitech International of Montreal, Canada, has developed a radar basedobstacle awareness system named OASYS which was presented at the QuebecHeliExpo 2001. While it is proposed that OASYS can detect smallobstacles, such as power lines, for example, up to two kilometers awayeven in adverse weather conditions, it is a rather heavy, bulky andcostly unit, which may render it prohibitive for small aircraft usage.

Another obstacle awareness warning system is being developed by DornierGmbH, in its Defense and Civil Systems Business Unit of Friedrichshafen,Germany under the tradename of HELLAS (Helicopter Laser Radar). In thisunit, a laser beam is sequentially scanned through a line series ofapproximately one hundred optic fibers to create a raster line scanwhich is projected from the system. The line scan is steered verticallyby a pivoted, oscillating mirror. The field-of-view is approximatelyplus and minus 32 degrees in azimuth and elevation with respect to aline of sight of the system. While Dornier promotes HELLAS as being aneffective obstacle detection unit, it remains a relatively narrow fieldof view device that is rather complex and costly. In addition, the largenumber of optic fibers required for effective obstacle detectionresolution, appears to render the device difficult to repeatedly alignwhich may lead to manufacturing difficulties.

Another problem encountered in these low-level flight profile aircraftapplications is the wind or air flow conditions surrounding the aircraftwhile it is carrying out its tasks. In some cases, an aircraft mayencounter substantially different air-flow conditions from side to side.For example, when flying in a canyon, the aircraft may have a mountainwall on one side and open spaces on the other. Landing on the flightdeck of an aircraft carrier poses similar risks. Such uneven air flowconditions may have an adverse affect on the responsiveness of theaircraft to the avoidance of detected obstacles.

Accordingly, it is desireable to have a wide field scanning laser basedobstacle awareness system which is simpler in design and less costlythan its predecessors to render it an economically attractive safetysystem for low-level flight profile aircraft. Combining air flow andobstacle measurements in a common system would provide the knowledge ofair conditions surrounding the aircraft when an obstacle is detected inits flight path allowing a pilot to make his avoidance decisions basedon such air data information. An enhanced situational awareness displaywould augment the peripheral vision of the flight crew to potentialcollision obstacles. The present invention is intended to provide forthese desirable features in a laser based obstacle awareness system aswill become more evident from the description thereof found hereinbelow.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, A wide fieldscanning laser obstacle awareness system (LOAS) comprises: a pluralityof first optical elements configured to direct a portion of a pulsedlaser beam generated by a light source to a light detector, and todirect the pulsed laser beam to a beam expander wherein the pulsed laserbeam is expanded; and at least one rotationally operated second opticalelement for directing the expanded pulsed laser beam from the systemwith a predetermined pattern scanned azimuthally over a wide field, theat least one rotationally operated second optical element also forreceiving reflections of the pulsed laser beam from at least one objectalong the predetermined pattern and directing them to the laser beamexpander wherein the laser beam reflections are focused; the pluralityof first optical elements also configured to direct the focused laserbeam reflections to the light detector for use in determining thelocation of the at least one object.

In accordance with another aspect of the present invention, the widefield scanning laser obstacle awareness system (LOAS) is used on-boardan aircraft for alerting an operator of obstacles posing a risk ofcollision with the aircraft. For this purpose, the system additionallycomprises: means for determining substantially the azimuth position ofthe directed pulsed laser beam; means for determining substantially theelevation of the directed pulsed laser beam; display apparatus; andwherein the processor means is coupled to the light detector, displayapparatus, azimuth position determining means and elevation determiningmeans for determining the location of the at least one object in range,azimuth and elevation in relation to a flight path of the aircraft, theprocessor means for driving the display apparatus to display anindication representing the at least one object in range, azimuth andelevation.

In accordance with yet another aspect of the present invention, Opticalscanning apparatus controllable to project a plurality of differentoutput scan patterns of a laser beam comprises: a first rotationallyoperated optical element for directing a laser beam, incident to asurface thereof, therefrom with an intermediate scan pattern; and asecond rotationally operated optical element for directing the laserbeam with the intermediate scan pattern from the apparatus with adesired output scan pattern, the first and second optical elementsadjustably rotationally operated in relation to each other to effect thedesired output scan pattern of the plurality of different output scanpatterns of the laser beam.

In accordance with yet another aspect of the present invention, thescanning laser obstacle awareness system (LOAS) additionally comprises:a mirrored optical element disposed in the path of the pulsed laser beambetween the plurality of first optical elements and the laser beamexpander, the mirrored optical element rotationally operated about anaxis thereof to effect a dithering of the pulsed laser beam beforeentering the laser beam expander wherein the dithered pulsed laser beamis expanded; the mirrored optical element and plurality of first opticalelements also configured to direct the focused laser beam reflections tothe light detector for use in determining the location of the at leastone object.

In accordance with yet another aspect of the present invention, the widefiled scanning LOAS comprises: at least one scan head, each scan headincluding the laser beam expander; and at least one rotationallyoperated second optical element for directing the expanded pulsed laserbeam from the scan head with the predetermined pattern, the at least onerotationally operated second optical element being rotated azimuthallyby the scan head to scan the predetermined pattern over a wide azimuthfield, the at least one rotationally operated second optical elementalso for receiving reflections of the pulsed laser beam from at leastone object along the predetermined pattern and directing the laser beamreflections to the laser beam expander wherein the laser beamreflections are collected and returned to the plurality of first opticalelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematic of a wide field scanning laserobstacle awareness system (LOAS) suitable for embodying at least oneaspect of the present invention.

FIG. 2 is a graph of an exemplary scan pattern generated from the LOASembodiment of FIG. 1.

FIG. 3 is a block diagram schematic of a light beam scan patterngenerator/receiver suitable for use in the embodiment of FIG. 1.

FIG. 4 is an illustration of an exemplary environment in which the LOASembodiment of FIG. 1 may operate.

FIGS. 5A and 5B are time graphs exemplifying the signal processing ofthe LOAS embodiment of FIG. 1.

FIG. 6 is a flowchart illustrating an exemplary programmed operation ofa processor suitable for use in the LOAS embodiment of FIG. 1.

FIGS. 7A and 7B are sketches illustrating an exemplary ditheringoperation of a perturbation mirror suitable for use in the embodiment ofFIG. 1.

FIGS. 8A and 8B are sketches illustrating the effects of a predeterminedangle tilt of the perturbation mirror on an image projected in space.

FIG. 9 is a sketch of two rotationally operative optical elementssuitable for use in embodiment of FIG. 1 for effecting a variety of beamscan patterns.

FIGS. 10A-10C are illustrations of exemplary beam scan patterns that maybe effected by the rotationally operative optical elements of theembodiment of FIG. 9.

FIG. 11 is a sketch of a light indicator display suitable for use in theembodiment of FIG. 3.

FIG. 12 is a sketch of an exemplary screen of a multi-function videodisplay (MFD) alternately suitable for use in the embodiment of FIG. 3.

FIGS. 13A-13E are plan view illustrations in time progression (timeslices) of an aircraft approaching obstacles near and in its flight pathshown by way of example.

FIGS. 14A-14E are illustrations of exemplary MFD screen displays of thetime slices of FIGS. 13A-13E, respectively.

FIG. 15 is a block diagram schematic of a combined LOAS and LIDAR systemsuitable for embodying another aspect of the present invention.

FIG. 16 is a sketch of a rotationally operative optical element suitablefor use in the embodiment of FIG. 15 for directing two beams from thecombined system with different predetermined scan patterns.

FIG. 17 is a sketch of a block arrangement of optical elements of aLIDAR system suitable for embodying another aspect of the presentinvention.

FIG. 18 is a sketch of an alternate block arrangement of opticalelements of a LIDAR system.

FIG. 19 is a block diagram schematic of a LIDAR system for determining3-axis flow velocity suitable for embodying yet another aspect of thepresent invention.

FIGS. 20, 20A and 20B illustrate functionally by way of example theprocessing involved in determining the 3-axis flow velocity by theembodiment of FIG. 19.

FIG. 21 is an illustration of an embodiment of the present inventionmounted to an aircraft with it own coordinates.

FIG. 21A depicts a set of three equations suitable for use intransforming a 3-axis flow velocity from one coordinate system toanother.

FIG. 22 is an exemplary program organization for use in programming aprocessor for determining a 3-axis flow velocity measurement.

FIG. 23 is an exemplary software flow diagram of a main program suitablefor use in the program organization of FIG. 22.

FIG. 24 is an exemplary software flow diagram of a foreground functionroutine suitable for use in the program organization of FIG. 22.

FIG. 25 is an exemplary software flow diagram of a clock functioninterrupt service routine (ISR) suitable for use in the programorganization of FIG. 22.

FIG. 26 is an exemplary software flow diagram of a trigger function ISRsuitable for use in the program organization of FIG. 22.

FIG. 27 is an exemplary software flow diagram of a serial function ISRsuitable for use in the program organization of FIG. 22.

FIG. 28 is an exemplary software flow diagram of an evaluate functionroutine suitable for use in the program organization of FIG. 22.

FIG. 29 is an exemplary software flow diagram of a velocity functionroutine suitable for use in the program organization of FIG. 22.

FIG. 30 is an exemplary software flow diagram of an output functionroutine suitable for use in the program organization of FIG. 22.

FIG. 31 is a block diagram schematic of a combined LOAS and LIDAR systemwherein the scan optical elements are embodied in a scan head inaccordance with another aspect of the present invention.

FIG. 32 is a sketch of an embodiment of a scan head suitable for use inthe embodiment of FIG. 31.

FIG. 33 is an illustration of the scan optical elements disposed in thescan head embodiment of FIG. 32.

FIG. 34 is an illustration of a LOAS embodying multiple scan heads inaccordance with another aspect of the present invention..

FIG. 35 is an illustration of an exemplary optical switch suitable foruse in the embodiment of FIG. 34.

FIG. 36 is an illustration of a combined LOAS and LIDAR system embodyingmultiple scan heads in accordance with another aspect of the presentinvention.

FIGS. 37 and 37A are isometric and cross-sectional illustrations,respectively, of a fiber optic cable which is suitable for use in theembodiments of FIGS. 31 and 34.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram schematic of a wide field scanning laserobstacle awareness system (LOAS) suitable for embodying at least oneaspect of the present invention. Referring to FIG. 1, a light source forgenerating a pulsed bean of light is comprised of a laser driver circuit10 and a laser source 12 which is driven by the circuit 10. In thepresent embodiment, the laser source 12 comprises a micro chip laserdiode which may be of the type manufactured by Nanolase bearing modelnumber NP-10320-100, for example. The laser source 12 is driven by thecircuit 10 to emit a pulsed light beam with a pulse width ofapproximately one to two nanoseconds (1-2 nsec.) or longer, and at apulse repetition rate on the order of ten kilohertz (10 kHz) or more.The light beam of the present embodiment is generated with a diameter ofapproximately three hundred micrometers (300 microns), with a wavelengthof fifteen hundred and fifty nanometers (1550 nm) or one thousand sixtyfour nanometers (1064 nm), for example, and in a state of linearpolarization. The laser source 12 may include beam conditioning optics(not shown) for collimating and enlarging the laser beam diameter from300 microns to three millimeters (3 mm).

The pulsed laser beam of light is guided over an optical path 14 to apolarizing beam splitter optical element 16 which passes most of thepulsed beam 14 along an optical path 18 to the input of a laser beamexpander 20. A small amount of the pulsed beam 14 is reflected by thebeam splitter 16 to a light detector 22 along an optical path 24 to actas a transmission time synchronization pulse as will become more evidentfrom the further description found herein below. In the presentembodiment, the light detector 22 comprises an avalanche photodiode(APD) which may be of the type manufactured by Analog Modules bearingmodel number 756, for example, and may include a variable gain circuitfor increasing sensitivity to pulses of small amplitude. In addition,the beam splitter 16 may include a quarter wavelength (λ/4) plate at theoutput thereof which converts the linearly polarized beam passed by thebeam splitter 16 to a circularly polarized beam which is passed alongoptical path 18 to the beam expander 20.

In the present embodiment, the circuit 10, laser source 12, lightdetector 22 and beam splitter 16 are all mounted on an optical bench 26in a proper alignment to create the optical paths 14, 18 and 24, forexample. The optical bench is then affixed structurally to a mountingstructure 28 which supports the entire LOAS in the present embodiment.The laser beam expander 20 which may be of the type manufactured bySpecial Optics bearing model number 52-71-10X-905-1064, for example, isalso mounted to the structure 28 such that its input or entranceaperture is aligned with the optical path 18 to receive the pulsed beamfrom the beam splitter 16. The beam expander 20 enlarges the diameter ofthe pulsed light beam with a 10× magnification, for example, and passesthe enlarged pulsed collimated light beam along an optical path 30 to atleast one rotationally operated optical element 32 for directing theexpanded pulsed laser beam from the LOAS along an optical path 36 with apredetermined pattern scanned azimuthally over a wide field. Aconventional fold mirror optical element 34 may be mounted to thestructure 28 and aligned for guiding the expanded light beam from theexpander 20 to the at least one rotationally operated optical element 32along the path 30. It is understood that the use of the fold mirror 34in the present embodiment is merely by design choice.

Pulsed light reflected along an optical path 40 from an obstacle orobject 38, like a wire, for example, along the predetermined pattern isreceived by the at least one rotationally operated optical element 32and directed back to the beam expander 20 along an optical path 42 viafold mirror 34. If there are more than one object in the path of thepredetermined pattern, then the LOAS will receive pulsed lightreflections from each of the detected objects. In the beam expander 20,the pulsed light reflections are collected into a condensed collimatedbeam in the vicinity of its input aperture. The light reflections fromthe object 38 are reversed in circular polarization from the transmittedlight beam. For example, if the transmitted beam was polarized with aclockwise polarization, then the light reflections would have acounter-clockwise polarization and vice versa. Aft optics in the opticalbench 26 guide the light reflections from the beam expander 20 along anoptical path 44 to the λ/4 plate and beam splitter 16. The λ/4 platereconverts the circularly polarized reflected light to linearlypolarized light at right angles to the transmitted light beam whichcauses the polarizing beam splitter to reflect the returned light pulsesto the light detector 22, which may be coupled to signal processingcircuits 50 that are also mounted to the common structure 28. Theoperation of the light detector 22 and circuits 50 in connection withthe detection of an obstacle will be explained in greater detail hereinbelow.

More specifically, in the present embodiment, the at least onerotationally operated optical element 32 comprises a first rotationallyoperated optical element 52 for receiving the expanded pulsed laser beamfrom the expander 20 and directing it to a second rotationally operatedoptical element 54 along optical path 56 with the predetermined patternas will become more evident from the following description. The secondelement 54 receives the pulsed light beam from the first element 52 anddirects the received beam with the predetermined pattern azimuthallyover a wide field which may be on the order of plus and minus ninetydegrees or more with respect to a reference axis of the LOAS. Pulsedreflections from objects along the predetermined pattern are directedfrom the second element 54 to the first element 52 over an optical path58. One or both of the elements 52 and 54 may be configured as foldmirrors.

The optical element 52 may be a rotating optical wedge which has onesurface inclined at a predetermined angle relative to an oppositesurface and is rotated about an axis normal to the opposite surface, ora wobble mirror rotated about an axis at a predetermined nutation anglefrom its normal axis (e.g. a Palmer scan mirror), for example, whereinthe expanded pulsed laser beam may be reflected from the mirroredsurface of the optical element with the predetermined pattern. In eithercase, the element 52 is coupled to and driven by a conventional highspeed circular scan module 60 which may include a drive system 62, likean electric motor, for example, and a conventional bearing system 64. Inthe present embodiment, the module 60 with its drive 62 and bearingsystem 64, which may be a Palmer mirror assembly, for example, ismounted to the common structure 28 and properly aligned thereon. Thedrive 62 rotates the element 52 about its intended axis at an angularspeed of approximately fifty (50) cycles per second, for example, whichcreates a cyclical conical pattern of pulsed laser beam projected fromthe LOAS via element 54.

Element 54 may also be a mirrored optical element which is driven by anazimuth scan motor 66, which may be a stepper motor, for example, torotate and scan the conical pattern of the element 52 azimuthallythrough an arc of approximately 180°, i.e. ±90° or more with respect tothe reference axis of the LOAS, over a time period of 0.5 seconds, forexample. Thus, the predetermined pattern will include an elevationvariation in relation to a line of sight axis of the system. Anexemplary scan pattern at 500 meters from the system is illustrated inthe graph of FIG. 2. Referring to FIG. 2, the reference axis of thesystem is shown by the vertical axis 70 and the line of sight axis ofthe system is shown by the horizontal axis 72. The helical-like line 74represents the scan pattern as it is being rotated by the first element52 and scanned azimuthally by the second element 54. In this example,the first element 52 is an optical wedge mirror with a wedge angle often degrees and rotated at approximately 115 Hz. The graph of FIG. 2only depicts an azimuth translation from 0° to +90°. It is understoodthat the azimuth translation from −90° to 0° would appear as the mirrorimage to what is depicted in FIG. 2. The azimuth scan rate of theillustration of FIG. 2 is approximately 2 Hz.

Note that with each scan pattern cycle of the illustration of FIG. 2,the light beam pattern 74 moves in elevation in relation to the line ofsight or horizontal axis 72 and in azimuth in relation to the referenceor vertical axis 70. Also, since the pattern 74 takes approximately 9msec. to complete a cycle and since the LOAS generates light beam pulseevery 0.1 msec., then there would be approximately 90 light beam pulsesuniformly generated per scan pattern cycle. As will become more evidentfrom the following description, the LOAS of the present embodiment maydetermine a location of each detected obstacle along the path of thepredetermined scan pattern in range, azimuth, and elevation.

Returning to FIG. 1, in the present embodiment, the azimuth scan mirroroptical element 54 is coupled to the azimuth scan motor 66 in a scanmounting assembly 68 which is also mounted to the common structure 28via the scan module 60, for example. Accordingly, all of the elements ofthe present embodiment may be mounted and fixedly aligned on the commonmounting structure 28. In some systems, an element of the LOAS may beadjustably realigned at its mounted position from time to time shouldthe need arise. In addition, while the present embodiment is describedas having two rotationally operated optical elements 52 and 54, it isunderstood that it is possible to combine the scan pattern and theazimuth rotations into one optical element which is driven by twomotors, one for the cyclical scan pattern and the other for the azimuthscan without deviating from the broad principles of the presentinvention. Also, more than two mirrors may be used as will be describedin connection with an alternate embodiment herein below. In addition, asingle mirror can be used to scan in elevation, using a resonantoscillating motion of the mirror in the vertical plane, for example,while simultaneously being driven in azimuth by a motor, producing araster scan pattern.

A block diagram schematic of a wide field light beam scan patterngenerator/receiver suitable for use in the present embodiment is shownin FIG. 3. Like reference numerals will be maintained for those elementsalready described for the embodiment depicted in FIG. 1. Referring toFIG. 3, electrical signals generated over signal line 78 by thephotodiode 22 are representative of received light beam reflections fromobjects along the predetermined pattern of the transmitted pulsed lightbeam. FIG. 4 illustrates an exemplary environment in which the LOASembodiment may operate. Referring to FIG. 4, the pulsed light beamprojected from the LOAS along the path 36, for example, may be reflectedfrom such obstacles as a cable 80, cable support towers or structures 82and background clutter which may take the form of trees and bushes 84,for example. The light reflections from the obstacles are received bythe LOAS and directed to the light detector 22 as described inconnection with the embodiment of FIG. 1 wherein the light reflectionsare converted to electrical signals representative thereof.

The time graph of FIG. 5A is illustrative of such electrical signalsproduced by the light detector 22 from the pulsed light beam reflectionsduring an interpulse period of the transmitted pulsed light beams. FIG.5A illustrates only the first approximately ten microseconds of a onehundred microsecond interpulse period, for example. In FIG. 5A, thefirst pulse 90 may be representative of the transmitted beam for timesynchronization; the second pulse 92 which is close in range may be justan electrical noise pulse; the third pulse 94 may be representative of areflection from a first obstacle, like the cable 80 or structure 82 asshown in the illustration of FIG. 4, for example; and the fourth pulse96 may be representative of a reflection from a second obstacle furtherin range, like one of the trees 84, for example.

Referring back to FIG. 3, the electrical signals from the photodiode 22over signal line 78 may be coupled to one input of a circuit 86 which isconfigured as a comparator circuit. An electrical signal representativeof a threshold level may be coupled to another input of the comparator86 for comparison with the electrical signals from the photodiode 22.The threshold level is shown by the dashed line 98 in FIG. 5A. FIG. 5Bis a time graph which exemplifies the operation of the comparator 86 inresponse to incoming electrical signals from the photodiode 22. Forexample, as pulse 90, the sync pulse, exceeds the threshold 98, theoutput of the comparator 86 is caused to change state from a highpotential (+5V) to a low potential (+2V). Note that in the embodiment ofFIG. 3, the output of the comparator 86 is coupled to a signal processor88 which may be part of the signal processing electronics 50. Theprocessor 88 may be a digital signal processor of the type manufacturedby Texas Instruments bearing model number TMS-320C6711, for example.Accordingly, the processor 88 may be programmed to detect the change instate at 100 in the time graph of FIG. 5B caused by the sync pulse 90and measure the time of all subsequent detected pulses with respect tothe sync pulse or first change in state 100 of the comparator 86. In thepresent embodiment, the comparator 86 may have a predetermined responsetime before it may return its output to a high level to detect the nextpulse or detected obstacle. Thereafter, in the example of FIG. 5B, thecomparator changes state at 102 in response to pulse 94 representativeof the detection of one obstacle and again at 104 in response to pulse96 representative of another obstacle. Note that no change of stateoccurs in response to pulse 92 which falls below the threshold level 98,and thus, is considered electrical noise. With preprogrammed data of thespeed of light, the processor 88 may be also programmed to determine therange to a detected obstacle from the time difference between the syncpulse and the pulse representative of the obstacle. The processor mayalso determine the azimuth and elevation location of the obstacle aswell, as will be described in connection with the following paragraphs.

Referring back to FIG. 3, the scan pattern module 60 may be coupled toand drive the rotationally operated optical element 52 through a shaft110 which may include an indication of its angle position with respectto a reference angle. In one embodiment for sensing the angular positionof the optical element 52, the shaft may be marked with indiciarepresentative of its relative angle or include a wheel thereon orattached thereto with such angle markings. In either case, the indiciamay be read by a conventional reader and digitally provided to theprocessor 88 as a measure of the angle of rotation of the scan patternoptical element. Thus, the processor will have stored at any time themeasured angle of the scan pattern which it may use to calculate azimuthand elevation of a detected obstacle. In another embodiment, the shaft110 may include markings like grooved teeth, for example, or haveaffixed thereto a wheel with teeth grooved therein. A conventionalproximity device 112 may detect each grooved tooth and generate anelectrical pulse in response. These electrical pulses may be counted ina counter 114 which count may be a measure of the current scan patternangle of optical element 52. The element 52 may include a mechanical,proximity or optical switch positioned to generate a reference pulse 116each time the element 52 is rotated past the reference angle. Thereference pulse 116 may be coupled to the counter 114 to reset it tozero so that it may start counting with respect to the reference anglewith each rotation cycle. Accordingly, as the processor 88 detects anobstacle in time, it may read the contents of the counter 114 which is ameasure of the concurrent angular position of the optical element 52 andfrom which the processor may determine elevation of the detectedobstacle.

In yet another embodiment for sensing angular position of the scanpattern, the processor 88 may include a clock of a predetermined ratefor counting up in a designated register thereof a count that is a timebased measure of the angular position. The reference pulse 116 may beprovided to the processor for resetting the count in the designatedregister. Each time the reference pulse 116 is received, the processor88 saves the total count in the counting register and resets theregister to start counting up from a zero count. In this embodiment,when an obstacle is detected, the processor 88 merely reads theconcurrent count in the counting register and compares it to the savedtotal count to obtain a ratio from which it may determine the angularposition of the scan pattern. The elevation of the obstacle with respectto the line of sight of the LOAS may be determined by taking, forexample, the sine of the sensed scan pattern angle of the detectedobstacle and multiplying it by the maximum elevation amplitude at themeasured range of the detected obstacle. That is, one half of thediameter of the plane section of the conical scan pattern at the rangeof the detected obstacle will be the maximum elevation amplitude. Thisis illustrated in the scan pattern example of FIG. 2 for a range of 500meters.

The embodiment of FIG. 3 also exemplifies a way for determiningsubstantially the azimuth position of the directed pulsed laser beam fordetermining the location of a detected object in at least range andazimuth. Referring to FIG. 3, a conventional digital clock circuit 120generates a clock signal 122 at a predetermined rate. Signal 122 iscoupled to select logic circuitry 124 and to a rate divider circuit 126which divides the rate of clock signal 122 by a factor N. The dividedrate signal 128 from the circuit 126 is coupled to the select logiccircuitry 124 and to an azimuth position counter 130 which increases itscount with each received pulse. The select logic circuitry 124 generatesa clockwise signal (CW) and a counter-clockwise signal (CCW) for use incontrolling the electric motor 66, which may be a stepper motor, forexample. The motor 66 is coupled to the azimuth scan mirror assembly 54by a shaft 132 for rotating the mirrored element 54 through its 180°rotation. The azimuth mirror assembly 54 may include a first switchpositioned to activate and generate a START signal at substantially the0° azimuth position, and a second switch positioned to activate andgenerate a STOP signal at substantially the 180° azimuth position, forexample. The START and STOP signals are provided to the select logiccircuitry 124. In some applications, the signal processor 88 may becoupled to the divider circuit 126 over signal line 134 for setting thenumber N by which the rate of signal 122 will be divided. The signalprocessor 88 is also coupled to the counter 130 over signal line 136 forreading the azimuth position count thereof.

In operation, the signal processor 88 may set the number N of thedivider 126 which ultimately sets the rate at which the laser beam scanpattern is rotated azimuthally. It is understood that this number N maybe preprogrammed into the rate divider circuit 126 as well. So, theselect logic 124 receives both a fast rate signal 122 and a slower ratesignal 128 and selects one of the rate signals to control or step themotor 66 through its rotation. For example, when the select logic 124receives the START signal from the scan mirror assembly 54, it selectsthe slow rate signal 128 to control the motor 66 via the CW control lineto rotate clockwise through its 180° rotation in a predetermined time,like 0.5 seconds, for example. When the STOP signal is generated, theselect logic 126 responds by selecting the fast rate signal 122 tocontrol the motor 66 via the CCW signal to rotate counterclockwise backto its starting position whereupon the process is repeated. It isunderstood that the azimuth scan may be controlled to rotate at theslower rate in a counterclockwise rotation and returned to its startingangular position at a much faster rate as well without deviating fromthe broad principles of the present invention.

Each time the select logic receives the START signal, it generates aZERO signal to the counter 130 for resetting the count thereof to zero.The STOP signal may be also coupled to the signal processor 88 whichresponds to the signal by reading and storing the total count in thecounter 130 which is representative of an azimuth angular position of180°, for example. So, each time an obstacle is detected by the signalprocessor 88, it may read the concurrent count in the azimuth positioncounter 130 and use the read count together with the total count todetermine the azimuth position of the detected obstacle. In the presentembodiment, the circuits 120, 124, 126 and 130 may be part of the signalprocessing circuitry 50. It is understood that the functions of thesecircuits may also be programmed into the signal processor 88.

In some applications, the azimuth scan may be controlled to rotate atthe programmed rate for both of the clockwise and counterclockwisedirections in which case, the counter 130 will count up from thestarting position in one direction and count down from the stop positionin the opposite direction. In these applications, the counter may stillbe reset to zero by the select logic 124 in response to the START signaland the processor 88 may read the total count of the counter 130 inresponse to the STOP signal. And, similarly, each time an obstacle isdetected by the signal processor 88, it may read the concurrent count inthe azimuth position counter 130 and use the read count together withthe total count to determine the azimuth position of the detectedobstacle.

The flowchart of FIG. 6 illustrates a programmed operation of the signalprocessor 88 by way of example. Referring to FIG. 6, the diode lasersource 12 may be controlled to fire periodically at a rate of 10 KHz or10,000 pulses per second, for example, with an interpulse period of 100μsec. autonomously by the driver circuit 10 or may be controlled to fireby the programmed processor 88 as shown by the block 140. In eithercase, the processor detects the sync pulse as described supra and startsa processor range timer in block 142. Thereafter, the processor beginssearching for return pulses of reflections from the targets or obstaclesalong the predetermined scan pattern in block 144. When a return pulseis received in block 146, which is representative of a detectedobstacle, the processor bins the return signal according to its time offlight in block 148. That is, the return pulse is indexed and stored ina designated memory location of the processor along with its recordedrange processor time which is the count in the timer concurrent with thetime of detection. This count is representative of the range of thedetected obstacle. Concurrent with the detection of the obstacle, theinstantaneous positions of the Palmer scan pattern and azimuth mirrorsare recorded as described supra, preferable in the designated memorylocation for the indexed detected obstacle, in block 150. Each time anobstacle is detected by the processor in the interpulse period of laserfiring, the blocks 146, 148 and 150 are repeated and the obstacle indexand its range and location representative data for azimuth and elevationare recorded in a designated memory location or bin.

After, the initial approximately 6 μsec. of the interpulse periodbetween laser firings or some other appropriate initial time periodends, the processor stops searching for detected obstacles in block 152.Thereafter, the processor may use the remaining time before anotherlaser firing to compute the range and location in azimuth and/orelevation for each obstacle detected and indexed in the currentinterpulse period from the recorded data thereof. In block 158, thisrange and position location information for the detected obstacle(s) maybe configured for display and transferred to a display 154 such as shownin the block diagram schematic of FIG. 3, for example. This informationmay also be provided by the processor 88 over a signal line 156 to othersystems for use therein. At the end of the interpulse period, the lasersource 12 may be controlled to fire again in block 140 and the processas just described is repeated. In this manner, each obstacle along thepredetermined scan pattern may be detected and its location determinedand the detected obstacles and their respective locations may bedisplayed to an operator for awareness purposes as will become moreapparent from the description found herein below.

The wide field scanning LOAS embodiment described in connection withFIGS. 1-6 detects obstacles along a predetermined scan path using apulsed laser beam spot size on the order of a meter in diameter at abouta kilometer in range, for example. As shown by the pattern example ofFIG. 2, obstacles will not be detected in the cusp areas between thescan paths of the pattern 74. To improve the obstacle detectioneffectiveness of the wide field LOAS embodiment, a beam perturbation ordither mirror may be disposed in the optical path 18 between the beamsplitter 16 and input or entrance aperture of the expander 20,preferably in the aft optics of the optical bench 26, for example. Theperturbation mirror 160 as shown in FIGS. 7A and 7B, which is configuredas a fold mirror, may be supported on a pivot and rotated back and forthacross a center axis of the optical path 18. In so doing, it will changethe beam approach angle into the entrance aperture of the beam expander20. For example, in the present embodiment, a ±1° pivot or tilt of theperturbation mirror 160 with respect to the central axis of the opticalpath 18 is expected to move the laser beam spot ±5 meters at a kilometerin range. If the mirror is dithered in this manner at a high rate, likeon the order of one to ten Kilohertz (1-10 kHz), for example, the 1meter laser beam spot size would be smeared to become effectively 5meters at 1 kilometer. Accordingly, a greater percentage of the scenewould be observed by an effectively wider laser beam spot size. That is,the width of the path of the scan pattern would be increased effectivelyfive fold.

FIGS. 7A and 7B illustrate by way of example the dithering operation ofthe perturbation mirror 160. In FIG. 7A the mirror 160 is at shownconfigured as a fold mirror pivoted about an axis 163 looking into thedrawing sheet. In FIG. 7A, the mirror 160 is shown at a zero angle tilt.Note that in this position of the mirror 160, the rays of the beamguided through the optical path 18 are centered about a central axis 162of the entrance aperture 164 of the beam expander 20. In FIG. 7B, themirror 160 is tilted or pivoted downward approximately 1° from its zeroangle position of FIG. 7A causing the rays of the beam to move off thecentral axis 162 downward at an approach angle to the entrance apertureof approximately minus one degree. Similarly, as the mirror 160 istilted upward 1° from the zero angle position, the rays of the beam willmove off the central axis 162 upward at an approach angle to theentrance aperture of approximately plus one degree. A rapid movement ofthe mirror 160 rotating between the ±1° tilt positions will result inthe effective spread of the laser beam spot along the scan pattern.

FIGS. 8A and 8B show the effect of the 1° tilt of the mirror 160 on animage projected in space. In FIG. 8A, the mirror 160 is at the zerodegree tilt position. Note that the laser beam reflected along path 18expands through the beam expander 20 as shown by the departing rays. Asthe beam exits the expander 20, it becomes collimated with parallel raysat path 30. The expanded collimated beam is reflected from mirror 52along path 56 to the mirror 54 where it is again reflected along path 36and directed from the system along the predetermined scan path. Tobetter illustrate the effects of the dithering of the perturbationmirror 160 on a projected image, like the spot size, for example, aconverging lens 168 is disposed at the output of the system to focus thebeam to a focal point or spot 170 in space a predetermined range fromthe system. This converging lens 168 is used in the present examplemerely for image analysis purposes. In FIG. 8B, the mirror 160 is tilteddownward 1° causing the collimated beam exiting the expander 20 to shiftdownward which results in a deflection of the focal spot to a newposition 172 that is only slightly away from the original focal position170 as shown in FIG. 8A. In the present example, a 1° tilt resulted inonly a 1.6 meter deflection of the focal spot at a range of onekilometer. Thus, a minor perturbation of the mirror 160 will not resultin substantial defocusing or distortion of an obstacle image detected atsubstantial distances from the system.

A perturbation mirror 160 suitable for use in the embodiment of FIG. 1may be any one of a variety of commercially available mirrors, like aPalmer or wobble mirror assemble or a scan mirror, for example. But toeffect the speeds of pivoting or dithering desired for the presentembodiment which may be on the order of 200-600 Hz, for example, amirror assembly that has a low inertia, like a mirror assembly madeusing micro electro-mechanical systems (MEMS) technology, is preferred.These type of low inertia mirror assemblies may use a smallpiezoelectric power supply. The area of mirrored surface of theperturbation mirror 160 may be made quite small, like on the order ofthe width of the laser beam it is reflecting. Several commerciallyavailable “fast” dither mirrors operated by piezoelectric drivers foroptical image stabilization would be suitable for this purpose.

In accordance with another aspect of the present invention, therotationally operative scan optical element 52 may comprise tworotationally operative scan mirrors 174 and 176 configured as foldmirrors with respect to each other as shown in the illustration of FIG.9 to project a plurality of different output scan patterns of the laserbeam along the optical path 56 to the azimuth scan mirror 54 wherein thescan pattern is steered azimuthally through a wide field as describedherein above in connection with the embodiment of FIGS. 1-6. A singlescan mirror 52 generates the helical pattern 74 when steered across thewide azimuth field as illustrated in FIG. 2. But, this pattern may notbe an ideal or a preferred scan pattern for the application at hand.Therefore, it would be desirable to have the option of tailoring anappropriate scan pattern for a particular application or be able tochange the pattern due to varying conditions. The dual fold mirrorassembly of this aspect of the present invention permits the tailoringof a scan pattern by setting and/or varying the phase, direction androtational speed of one mirror 174 with respect to the other mirror 176.In the present embodiment, the mirrors 174 and 176 may comprise Palmeror wobble mirror assemblies, each rotationally operative at apredetermined nutation angle, like on the order of 5°, for example.However, it is understood that optical wedge type mirrors may beconfigured to function just as well without deviating from the broadprinciples of the present invention.

In the illustration of FIG. 9, the rotationally operative mirror 174 isconfigured for directing the laser beam which is incident to a surface178 thereof along optical path 30, for example, to the otherrotationally operative mirror 176 along an optical path 180 with anintermediate scan pattern. The other rotationally operative mirror 176is configured for directing the laser beam which is incident to asurface 182 thereof along path 180 to the azimuth scan mirror 54 overpath 56 with the desired scan pattern. The mirrors 174 and 176 areadjustably rotationally operative about respective axes of rotation 184and 186 in speed, direction and phase angle in relation to each other toeffect the desired output scan pattern of the plurality of output scanpatterns of the laser beam. In the present embodiment, an electricscanner motor may be coupled to each mirror and controlled to rotateeach mirror at a predetermined nutation angle (angle 188 for mirror 174,and angle 190 for mirror 176) with the desired speed, direction andphase angle in relation to the other mirror to effect the desired outputscan pattern. FIGS. 10A, 10B, and 10C illustrate exemplary scan patternswhich may be effected by the rotationally operative mirrors 174 and 176.Other scan patterns are also possible with different combinations ofrotations and speeds.

In FIG. 10A, a sawtooth scan pattern is shown generated by the dualmirror assembly embodiment of FIG. 9 by operating mirror 174 at arotational speed of 50 Hz in a clockwise direction with a nutation angleof 5°, and operating mirror 176 at a rotational speed of 50 Hz in acounter-clockwise direction in relation to mirror 174, with a nutationangle of 5°. In this example, the azimuth steering rate is approximately360° per second. This scan pattern may be better suited for detectingvertical or horizontal shaped obstacles. In FIG. 10B, a large circularscan pattern is shown generated by the dual mirror assembly embodimentof FIG. 9 by operating mirror 174 at a rotational speed of 50 Hz in aclockwise direction with a nutation angle of 5°, and operating mirror176 at a rotational speed of 50 Hz also in a clockwise direction, but180° out of phase to mirror 174, with a nutation angle of 5°. In thisexample, the azimuth steering rate is approximately 360° per second.Finally, in FIG. 10C, a small circular scan pattern is shown generatedby the dual mirror assembly embodiment of FIG. 9 by operating mirror 174at a rotational speed of 50 Hz in a clockwise direction with a nutationangle of 5°, and operating mirror 176 at a rotational speed of 50 Hzalso in a clockwise direction, but with a 22° phase difference to mirror174, with a nutation angle of 5°. In this example, the azimuth steeringrate is also approximately 360° per second. Accordingly, the size of thepattern, as shown by FIGS. 10B and 10C, may be varied by changing thephase angle of one mirror in relation to the other while maintaining therotational speed substantially fixed. It is also possible to change thedensity of the pattern in azimuth scan by altering the speed of theazimuth scan mirror. Note that the side edges of the patterns of FIGS.10A-10C appear somewhat compressed because the pattern is projected ontoa flat surface disposed directly in front of the system. The horizontaland vertical units shown in the Figures are normalized to a ±90° azimuthscan and a predetermined target range, respectively.

In accordance with yet another aspect of the present invention, the widefield scanning LOAS embodiment described above in connection with FIGS.1-6 may be disposed on-board an aircraft, like a helicopter, forexample, for use in alerting an operator or pilot of the aircraft ofobstacles posing a risk of collision with the aircraft. The processor 88described above in connection with the embodiment of FIG. 3 determinesthe location of one or more detected obstacles in range, elevation andazimuth in relation to a flight path of the aircraft and drives thedisplay 154 which may be located in the cockpit of the aircraft, forexample, to display to the pilot or an operator an indicationrepresenting the one or more obstacles or objects in range, azimuth andelevation. It is understood that the processor 88 may first determinethe location of a detected obstacle in relation to the reference axes ofthe LOAS and then, convert the location to the reference axes of theaircraft. This conversion from one set of reference axes to another willbe explained in greater detail herein below.

One embodiment of the display 154 comprises a panel 200 of lightindicators 202 as shown by the illustration of FIG. 11. The lightindicators 202 of panel 200 may be light emitting diodes (LEDs), forexample. In this embodiment, the panel 200 includes at least one row 204and at least one column 206 of indicators 202. The row 204 may representa horizontal axis of the flight path of the aircraft and the column 206may represent an elevation axis thereof. Accordingly, the indicator 208at the intersection of the row 204 and column 206 represents the line ofsight or instantaneous directional path of the aircraft. The lightindicators 202 may be controlled to emit light of different colors toindicate the location of the one or more objects in elevation andazimuth in relation to the flight path of the aircraft. A color changefrom green to yellow to red, for example, may indicate the range of adetected object from the aircraft. In the illustration of FIG. 11, thecolors are represented by gray scale. For example, a blackened indicator210 is indicative of red and indicates that the detected objectrepresented thereby is close in range to the aircraft, but below theaircraft. A gray indicator 212, for example, may represent a detectedobject at mid range to the aircraft, but substantially off to the leftthereof. Those indicators 202 which are not lit or are only slightlygray (green) represent no detected objects of detected objects far inrange from the aircraft, respectively. A change in color of an indicatoron the panel 200 may also indicate to the operator the risk of acollision of one or more detected obstacles with the aircraft.

Another embodiment of the display 154 comprises a multi-functional videodisplay (MFD), an exemplary screen of which being illustrated in FIG.12. The screen of the MFD may display a forward looking view, like theview shown in FIG. 12, for example, obtained from a video or forwardlooking infrared (FLIR) camera or radar unit (not shown) mounted to thefront of the aircraft. Generally, radar and video or FLIR cameras have arelatively narrow field of view, on the order of ± thirty degrees (±30°)in azimuth from the flight path of the aircraft, for example.Accordingly, the operator may view only those obstacles in the field ofview of the camera to ascertain risks from obstacles in the aircraft'spath. Note that in the screen of FIG. 12, the MFD displays a wirestretching horizontally across the path of the aircraft shown by thedotted line 216 which may change in color according to the detectedrange thereof. Note also that a variety of information obtained fromsensors on the aircraft or received from uplinked transmissions to theaircraft is displayed on the screen of FIG. 12 through use of overlay orimage integration technology which is well known to all those skilled inthe pertinent art. An exemplary MFD for use in the present embodiment ismanufactured by Goodrich Avionics Systems, Inc. under the tradename ofSmartDeck™ display. These type of MFDs display such information asaircraft velocity, i.e speed and heading, altitude, above ground level(AGL) readings, aircraft power levels and the like.

The present invention enhances the situational awareness of the pilot oroperator of the aircraft by displaying the locations of detectedobstacles in relation to the aircraft outside of the azimuth field ofview of the display screen of the MFD. It does this by overlaying animage in the form of at least one vertical bar 218 onto the screen imageof the MFD for representing one or more detected objects and thelocations thereof. In the present embodiment, one vertical image bar 218is overlaid to the far left of the screen image and another verticalimage bar 220 is overlaid to the far right of the screen image. Each bar218 and 220 is split into two areas, one area 222 above the center lineof the display screen, which is representative of the current altitudeof the aircraft, and the other area 224 below the center line. Each bar218 and 220 is controlled to light upon the detection of an objectazimuthally outside of the field of view of the MFD starting at thebottom area 222 with a color indicative of the range to the detectedobject. In the present embodiment, the LOAS may have a field of regardof 50 meters to 1 kilometer in range, ±90° in azimuth and ±10° inelevation, for example.

For example, as an object is first detected at a range far from theaircraft, but azimuthally outside the field of view of the MFD, thebottom of the corresponding bar 218 or 220 becomes lit with a greencolor indicting the elevation of the object is determined to beoptically below the altitude of the aircraft and at a far range thereto.As the aircraft approaches the detected obstacle, the image bar willchange in color, like from green to yellow, for example, to indicate achange in the range thereof and also may grow vertically in size if theelevation of the obstacle is determined to be optically closer to thealtitude of the aircraft. And, as the detected obstacle becomes veryclose to the aircraft in range, the color of the corresponding image barwill change from yellow to red, for example, and if the obstacle isdetermined to be above the altitude of the aircraft, the colored portionof the image bar will extend above the center line of the display screenin the portion 224 thereof. In this manner, the pilot or operator willbe alerted to detected obstacles outside of the azimuth filed of view ofthe MFD and their locations in range(color) and elevation (height ofbar) in relation to the aircraft.

FIGS. 13A-13E are plan view illustrations in time progression (timeslices) of a helicopter 228 containing a wide field scanning LOASsimilar in type to the foregoing described embodiments and including anMFD like the type described in connection with FIG. 12, for example,approaching an electrical power line 230 supported by poles 232 and a200 meter radio tower 234 and connecting support lines 236. Circledlines 238, 240 and 242 are representative of ranges 200 meters, 400meters and 600 meters, respectively, from the aircraft 228 which isheading in the direction of the arrow 244. The field of view of the MFDis shown by the wedged area 246 and may be on the order of ±15° inrelation to the flight heading 244 of the aircraft. Exemplary MFD screendisplays of the time progression illustrations of FIGS. 13A-13E areshown in FIGS. 14A-14E, respectively.

Referring to FIG. 13A, which is the first illustration in time, theaircraft 228 is shown at a range of greater than 600 meters from both ofthe power line and tower obstacles 230 and 234, respectively.Accordingly, since the power line 230 is partially within the field ofview (FOV) of the MFD, it is displayed as an overlaid dotted line in thescreen of FIG. 14A. But, since the obstacles 230 and 234 are outside ofthe 600 meter range, the vertical bar images 218 and 220 are not lit.The 600 meter range is set by design choice for the present example, andit is understood that this range may vary according the specificapplication at hand.. In the next time slice as shown in FIG. 13B, thehelicopter has moved closer to the power line 230, poles 232 and tower234 and a portion 248 of the power line 230 and poles 232 is within the600 meter range of the LOAS, albeit outside of the azimuth FOV 246 ofthe MFD. The obstacles 248 are detectable within an azimuth sector 250of the wide field scanning LOAS of the aircraft 228 and thus, aredisplayed in the vertical bar 220 with a color green, for example, andat a height 252 indicative of the determined elevation thereof which isshown in the exemplary screen display of FIG. 14B. In the presentexample, the color green illustrated by light gray is indicative of arange of a detected obstacle between 400 and 600 meters. Note that theheight 252 of the lit vertical bar 220 is below the center line of thescreen indicating to the operator that the obstacle is below thealtitude of the aircraft 228.

In the time slice of FIG. 13C, the aircraft 228 has moved closer to theobstacles to the point where a portion 254 of the power line and polesare within a range between 200 and 400 meters in azimuth sectors 250 and256. Upon detection by the LOAS of the aircraft 228, the vertical imagebar 220 as shown in FIG. 14C displays a green portion (white or lightgray) 252 representing the portion 248 of the power line and polesfalling between 400 and 600 meters in range, and a yellow portion(darker gray) 258 representing the portion 254 of the power line andpoles falling between 200 and 400 meters in range. The height 260 of thevertical bar image 220 of the screen of FIG. 14C reflects the elevationof the detected obstacles in relation to the altitude of the aircraft,i.e. center line of the screen. Note that the obstacle portion 254 isoutside of the azimuth FOV 246 of the MFD and would not be observed bythe pilot without the aid of the LOAS and its vertical bar image overlay220 onto the screen image of the MFD. Note also that the LOAS of theaircraft 228 detects the tower 234 in an azimuth sector 262 outside ofthe FOV 246 and lights the vertical bar image 218 as an indicationthereof, albeit beyond the 600 meter range.

In the time slice of FIG. 13D, the aircraft has moved closer to thepower line 230 and tower 234 and indicates this to the operator throughthe vertical bar images overlays 218 and 220 as shown by the screen ofcorresponding FIG. 14D. Note that the vertical bar image 218 hasincreased to the height 264 indicating that the obstacle is at anelevation close to the altitude of the aircraft 228 although more than600 meters in range. Also, the vertical bar image 220 has increased to aheight 266 beyond the center line of the display to indicate that thedetected obstacles in azimuth sectors 256 and 250 are at an elevationabove the altitude of the aircraft and the risk of a collision with suchobstacles has increased. In the time slice of FIG. 13E, the aircraft 228has moved even closer to the power line 230, a portion 268 of which nowdetected by the LOAS of the aircraft to be within 200 meters in range.In response, the LOAS lights the vertical bar image 220 with a red color(illustrated by dark gray) at a height 272 well beyond the center lineof the screen. This indicates to the pilot that the power line is within200 meters and at the altitude of the aircraft. In other words,collision of the aircraft 228 with the portion 268 of the power line isimminent unless immediate evasive action is taken. On the other hand,the LOAS of the aircraft also detects the tower 234 in an azimuth sector270 within 600 meters in range of the aircraft and indicates through thelighting of the vertical bar image 218, its range by color and elevationby height. Note that the vertical bar image 218 depicts the detectedelevation of the tower 234 approximately at the altitude of theaircraft, represented by the center line of the screen. So, the pilot isalso aware of the tower 234 and its range and elevation and can avoid itin the evasive action taken to avoid the power line portion 268.

Therefore, the foregoing description of FIGS. 13A-13E and 14A-14Eillustrate by way of example the operation of the wide field scanningLOAS in use on-board an aircraft and the enhanced situational awarenessit provides to the pilot and/or operator in the form of a dynamicallychanging display that extends beyond the visual field of view or a fieldof view of an MFD of the aircraft. Without the aid of the LOAS on-boardthe aircraft and the displayed overlaid images of detected obstacles andtheir locations with respect to the flight path and altitude of theaircraft, the pilot and/or operator of the aircraft may not be madeaware of the risk of imminent collision of the aircraft with suchobstacles and collision may not be otherwise avoided.

While the wide field scanning LOAS described above provides an enhancedawareness to the operator, the ability to avoid a detected obstacle inthe flight path of the aircraft may be further improved knowing the windconditions around the aircraft as well. So, combining a wide fieldscanning LOAS for detecting obstacles in the vicinity of the aircraftwith a laser air data system, like a light detection and ranging (LIDAR)system, for example, for measuring the wind velocity at points aroundthe aircraft and particularly, at the detected obstacle or at a launchpoint of a weapon for a military platform is desirable. A suitableembodiment of such a combined system is shown in the block diagramschematic of FIG. 15.

Referring to FIG. 15, the pulsed laser beam transmitting and receivingoptical elements of a LOAS is shown in the dashed line enclosed block280, the continuous wave (CW) laser beam transmitting and receivingoptical elements of a LIDAR system is shown in the dashed line enclosedblock 282, optical elements common to the LOAS and LIDAR systems 280 and282 are shown in the dashed line block 284. Like reference numerals willbe used for those elements already described in connection with the LOASembodiment of FIGS. 1-6 herein above. For example, in block 280, apulsed laser source of the present embodiment may comprise the elementsof the laser driver 10 and laser diode 12. Beam conditioning optics forcollimating and expanding the generated pulsed laser beam width alongoptical path 14 is shown by block 11. Beam splitter 16 and the quarterwavelength plate 17 pass the pulsed laser beam along path 18 with acircular polarization. A portion of the generated pulsed laser beam isreflected by the splitter 16 over path 24 to the light detector 22 whichmay be an APD, for example. The electrical signals generated by thelight detector 22 are provided to the threshold detector or comparatorcircuit 86 which is coupled to the processor 88. Azimuth position datamay be provided to the processor 88 in a similar manner as thatdescribed for the embodiment depicted by FIG. 3, for example.

In the LIDAR block or module of elements 282, a laser source 286 iscontrolled to generate a linearly polarized CW laser beam at awavelength substantially different from wavelength of the pulsed laserbeam of the LOAS elements 280. The LIDAR generated laser beam may be atone wavelength in the range of 850 to 1550 nanometers, for example, andthe LOAS laser beam may be at a different wavelength in the range of850-1550 nanometers, for example. However, it is understood that otherwavelength ranges may work just as well and the present invention is notlimited to any specific wavelength or wavelength range. The CW laserbeam is generated along an optical path 288 to beam conditioning optics290 which collimate and expand the CW beam before passing it along anoptical path to a polarizing beam splitter 294. Most of the linearlypolarized light is passed by the beam splitter 294 along path 296 to aone-quarter wavelength (λ/4) plate 298 which converts the linearlypolarized light to circularly polarized light before passing the beamalong an optical path to beam converging optics 300. Back at polarizingbeam splitter 294, a small portion, like on the order of 2% or so, ofthe generated CW beam is reflected along an optical path 302 to anacousto-optical modulator (AOM) 304 which shifts the frequency of thereflected beam by a predetermined frequency which may be on the order of80 MHz, for example. The reason for this frequency shift is to avoid adirectional measurement ambiguity as a result of the heterodyningoperation which will become more evident from the following description.The frequency shifted beam exiting the AOM 304 is optically guided alongan optical path 306 by one or more optical elements to anotherpolarizing beam splitter 308.

Reflected light from an aerosol particle, for example, at apredetermined distance from the combined system is returned throughoptics 300, the λ/4 plate 298, and along optical path 296 to the beamsplitter 294 wherein it is reflected along an optical path 310 to thebeam splitter 308. The returned beam is combined, i.e. heterodyned, withthe transmitted (shifted frequency) beam portion in the beam splitter308 to effect a light beam with a Doppler frequency content caused bythe reflection off of the particle in space. In the present embodiment,if the returned beam is unshifted in Doppler frequency, the heterodyningwill result in a combined light beam signal at the center frequency forheterodyne processing which may be set at 80 MHz, for example. Thus, ifthe returned beam is Doppler shifted, the heterodyning process willresult in a combined beam with Doppler frequency content of eithergreater than or less than 80 MHz. In this way, the process will not beconfused by negative Doppler frequency shifts caused by recedingtargets, which are indistinguishable from the positive Doppler frequencyshifts caused by approaching targets if the heterodyning light beam isunshifted in frequency. The combined beam with the Doppler frequencycontent is guided along an optical path 312 to a light detector 314which may be a photodiode, for example. The photodiode 314 converts thecombined light beam into a time varying analog electrical signal 316which is passed on to the processor 88 via signal conditioning circuit318. If the processor 88 is a digital signal processor, the time varyinganalog signal 316 may be digitized by the signal conditioning circuit318 according to a predetermined sampled data rate for processing by theprocessor 88.

The beam converging optics 300 may be a variable laser air data rangemodule which includes a group of focusing elements that permitsadjustably setting the focal point for the LIDAR generated beam at aspot in space which may vary from say 5 meters to 20 meters, forexample, from the system. This focal spot is space is where the beamreflections from one or more particles flowing in space areconcentrated. In one embodiment, the optics 300 includes the selectionof a particular focusing lens to effect the desired distance to thefocal spot in space. Each different lens will provide for focusing to aspot in space a discrete predetermined distance or range from thesystem. This lens selection process may be performed manually byplugging in the desired focusing lens or electro-mechanically byapparatus comprising a mechanical carousel having different lens, forexample, which carousel may be controlled to rotate to the selectedfocusing lens. In another embodiment, the optics 300 may include a lenswhich is electronically controlled to change its focusingcharacteristics to effect the desired range of the focal spot in space.

In the common optical elements block or module 284, the coherent CWlight beam exiting the optics 300 is guided along an optical path 319 toa dichroic filter optical element 320. The pulsed coherent light beamalong optical path 18 is also guided to the dichroic filter 320. Withproper alignment, the two coherent light beams of different wavelengthsmay be guided to the dichroic filter 320 such that one is reflected andthe other is passed along a common optical path 322 towards the entranceaperture of the beam expander or telescope 20 which is aligned to acceptand expand the two coherent beams and exit the expanded coherent beamsalong another common optical path 324 at an output thereof. The expandedcoherent beams are guided along common path 324 to be incident upon theat least one optical element 32 as described in connection with theembodiment of FIG. 1. The at least one optical element 32 in turndirects the two beams from the system into space. Reflections of the CWcoherent beam from particles at the focal spot and reflections of thepulsed coherent beam from obstacles are all returned to the at least oneoptical element 32 which receives such reflections and directs themalong path 324 back to the beam expander 20 wherein they are focused toa focal point of the beam expander 20 along path 322. The dichroicfilter 320 may be disposed in the vicinity of the focal point of thebeam expander 20 along path 322 to receive the focused reflections andseparate the focused light reflections corresponding to the pulsedcoherent beam from the focused light reflections corresponding to the CWcoherent beam based on the different wavelengths thereof.

Separated light reflections corresponding to the pulsed coherent beamare directed back to the LOAS module 280 along path 18 for use indetecting one or more objects as described in connection with theembodiments of FIGS. 1-6, for example. In addition, separated lightreflections corresponding to the CW coherent beam are directed back tothe LIDAR module 282 along path 319 for determining flow velocity aswill be more fully described. As has been described supra, the at leastone optical element 32 comprises at least one common rotationallyoperated optical element which may direct both of the CW and pulsedcoherent beams incident thereon from the system, the CW beam beingdirected from the system with a first predetermined pattern and thepulsed beam being directed from the system with a second predeterminedpattern. In the embodiment described above in connection with FIGS. 1-6,the at least one rotationally operative element 32 comprises opticalelements 52 and 54 which together may be configured and rotationallyoperated to direct both of the CW and pulsed coherent beamssubstantially colinearly from the system along path 36 with theazimuthally steered, conical beam pattern that is depicted in FIG. 2. Inthis manner, the first and second patterns will be substantially thesame and directed substantially to common azimuth positions in theazimuthal scan. An embodiment for directing the two coherent beams fromthe system with different first and second patterns will be describedherein below.

Separated light reflections that are guided along path 319 back to theLIDAR module 282 will pass through the beam converging optics 300 to theλ/4 plate 298 wherein the circularly polarized light is converted backto linearly polarized light and passed on to the beam splitter 294 overpath 296. However, since the circular polarization direction of thetransmitted beam is reversed upon reflection from a particle, theconverted linear polarization state of the reflected light will be atright angles to the linear polarization state of the transmitted beam.Accordingly, instead of being passed by the beam splitter 294, thereturned light reflections will be reflected along path 310 andheterodyned with the transmitted beam (shifted in frequency) in splitter308 as has been described herein above. The processor 88 may compute theflow velocity in the vicinity of the aircraft at various azimuthpositions from the time varying electrical burst signals converted bythe light detector 314 using Doppler signal processing, like FastFourier Transform (FFT) processing, for example, which is well-known toall those skilled in the pertinent art. The flow velocity may becomputed in one or more axes as will become more evident from thedescription found herein below. Azimuth position may also be determinedby the processor 88 from inputs of azimuth determining apparatus asdescribed in connection with the embodiment of FIG. 3, for example.Accordingly, flow velocity may be correlated with azimuth position inthe processor 88. And, since the light reflections of the CW beam andthe pulsed beam are at common azimuth positions in the presentembodiment, flow velocity may be computed at the azimuth position of adetected obstacle as well as in other azimuth positions.

In some applications, having the CW beam and pulsed beam directed fromthe system colinearly with substantially the same predetermined patternis not desirable, particularly where single dimensional flow velocitywill suffice. An exemplary embodiment for directing the two beams fromthe system with different predetermined patterns is shown in theillustrations of FIGS. 16 and 16A. In the embodiment exemplified in FIG.16, the rotational operative optical element 52 comprises a dichroicwedge optical element including a wedged surface 330 and a flat surface332. The optical element 52 may be rotated about an axis normal to theflat surface 332 shown by the dashed line 333. The wedged surface 330may be coated with a dichroic coating which has the characteristics ofpassing light substantially at the wavelength of the CW beam andreflecting light substantially at the wavelength of the pulsed beam, forexample. And, the flat surface 332 may be coated with a reflectivecoating, like gold or silver, for example, which reflects lightsubstantially at the wavelength of the CW beam. Referring to FIG. 16,the pulsed beam exiting from the beam expander 20 along path 324illustrated by the rays 334 is reflected from the wedged surface 330 ofthe optical element 52 with a conical pattern towards the mirroredoptical element 54 which steers the conical pattern of the pulsed beamazimuthally to effect a helical-like pattern such as the pattern 336shown in FIG. 16A. In addition, the CW beam exiting from the beamexpander 20 along path 324 illustrated by the rays 338 is passed throughthe wedged surface 330 of the optical element 52 to the flat surface 332where it is reflected towards the element 54. Note that no pattern isimparted to the CW beam because the reflective surface is flat and theoptical element 52 is being rotated about an axis normal to the flatsurface 332. Therefore, the optical element 54 will reflect and steerthe CW beam in a line pattern through an azimuthal scan like the pattern340 shown in FIG. 16A, for example. In this manner, the CW beam andpulsed beam may be directed from the combined system with two differentpatterns steered azimuthally.

While the foregoing described embodiment of FIG. 16 describes theoptical element 52 as including a wedged optical element, it isunderstood that other optical elements may be used to servesubstantially the same function. For example, a dichroic wobble mirrormay be used as optical element 52 for reflecting light of one wavelengthfrom one surface thereof and directing light of another wavelength fromanother surface thereof. Accordingly, there are a variety of othersimilar optical elements or combinations of optical elements that couldbe used as the element 52 just as well as the ones described to impartdifferent predetermined patterns for the CW and pulsed beams.(*) It isfurther understood that even a single rotationally operated opticalelement, wedged or otherwise, may be rotated and steered azimuthally toimpart the different predetermined patterns to the CW and pulsed beamswithout deviating from the broad principles of the present invention.

In accordance with yet another aspect of the present invention, theoptical elements of the LIDAR module 282 may be configured in a blockarrangement 350 such as illustrated in FIG. 17, for example. Referringto the embodiment of FIG. 17, the block 350 is comprised of a pluralityof glass modules, delineated by dashed lines, which are aligned togetherto form a plurality of optical paths in the block and secured togetherto maintain the alignment. The collimated light source 286, which maycomprise the laser diode 286 and beam conditioning optics 290 (see FIG.15), for example, may be secured to the block 350 for generating acoherent beam of light over at least one optical path 354 in the block350 which guides the coherent beam of light to an exit point 356thereof. The light detector 314 is also secured to the block 350 whichis operative to receive the return coherent beam of light over anoptical path 360 and configured to conduct the return coherent beam tothe light detector 314 over at lest one other optical path formedtherein. Accordingly, the block 350 may be disposed in a LIDAR systemon-board an aircraft as a whole and endure the shock and vibrationenvironment of the aircraft without substantial loss of alignment or atleast reduce the number of realignments over its lifetime. Thus, oncethe optical elements are secured in place, the alignment between theoptical elements of block 350 should be maintained.

Referring to FIG. 17, two of the glass modules 362 and 364 of theplurality are secured together, preferably by cementing, to form thebeam splitter 294 (see FIG. 15) that is disposed in the optical path 354for passing light in a first polarization state along an optical path366 to exit the block at point 356 and reflecting light in a secondpolarization state along an optical path 368. The quarter wavelengthplate 298 may be secured, preferably by cementing, to the block 350 atthe exit point 356 for converting the polarization of the exiting beamover path 360. The beam splitter 294 is also formed in the path 366 ofthe return coherent beam of light. Another pair of glass modules 370 and372 of the plurality are secured together, preferably by cementing, toform the beam splitter 308 that is formed in an optical path 374 of thereturn beam. The AOM 304 is disposed in a cavity 376 and secured inplace, preferably by cementing. Another module 378 of the pluralitycomprises a dove prism which is cemented to at least one other module380 of the plurality to form the optical path 368 that guides the lightreflected from the beam splitter 294 to the AOM. The dove prism 378includes polished surfaces 382 and 384 for forming the optical path 368by internal light reflections. Light exiting the AOM enters anotherglass module 386 which has a polished surface 388 for reflecting thelight exiting the AOM along an optical path 390 to the beam splitter308.

An alternate embodiment of a block arrangement 400 for the LIDAR opticalelements 282 is shown in the illustration of FIG. 18. Referring to FIG.18, the laser source 286 and optics 290 are secured to the block 400 atone side of a glass module 404 for generating a coherent beam of lightwhich is guided along an optical path 402 through the module 404. Asurface 406 of module 404 is cemented to a surface of another glassmodule 408 to form the beam splitter 294 in the path 402 of the coherentlaser beam. Light of one polarization state of the coherent beam ispassed through the beam splitter 294 and exits the block 400 at point410 where the λ/4 plate 298 is secured. Light of another polarizationstate of the coherent beam is reflected from the beam splitter 294 intoa dove prism glass module 412 which is cemented to the glass module 404.The dove prism 412 includes two polished surfaces 416 and 418 whichreflect the reflected light from the beam splitter 294 along an opticalpath 414. The AOM 304 is disposed and secured in an opening or cavity420 which is formed by the sides of the glass blocks 404, 408 and athird glass block 422. Light reflected from the polished surface 418 ispassed through glass module 404 and into the AOM 304. A beam correctionoptical element 424 may be affixed to the exit end of the AOM 304 tocompensate for or readjust the position and angle of the light beamexiting the AOM 304. A surface 426 of the glass module 422 is cementedto a like surface of the glass module 408 to form the beam splitter 308.One side 428 of the module 422 is polished to reflect the beam existingthe beam correction element 424 along an optical path 430 to the beamsplitter 308. The return beam along path 432 is converted to a linearpolarization state by the plate 298 and passed to the beam splitter 294wherein it is reflected along an optical path 434 through the module 408to the beam splitter 308 to be combined with the beam from path 430. Thecombined beam is directed along an optical path 436 through module 422to the light detector 314 which is secured to module 422.

Some or all of the glass modules of block 350 or block 400 may besecured together by cementing using an adhesive, preferably anultraviolet cured optical adhesive, for example. Note that for bothglass block embodiments, 350 and 400, the collimated light source 286 issecured to one side of the block and the exit point of the transmittedcollimated light beam is at another side of the block. In addition, thealignment of the glass modules of each block 350 and 400 forms a directline optical path between the collimated light source 286 and the exitpoint of the block. In addition, the light detector 314 of each blockembodiment 350 and 400 is secured to a side of the block other than theside to which the laser source is secured. Still further, the opticalpaths of the transmitted and return coherent light beams are co-linearwithin the block.

The illustrations of FIGS. 17 and 18 also depict by symbols the variouspolarization states of the light beams as they are guided along theirrespective optical paths. For example, the circled X symbol representslight in a state or plane of linear polarization going into the pageparallel to the optical path along which it is guided and thedirectional arrow symbol represents light in a state or plane of linearpolarization going into the page perpendicular to the optical path alongwhich it is guided, that is, at right angles to the circled Xpolarization state. Also, light in a circularly polarized state isdepicted by an arrowed rotation symbol, the direction of rotation isdepicted by the arrow. Knowledge of these polarization symbols willyield a better understanding of the operation of the optical elements ofthe exemplary block embodiments 350 and 400, which operation having beendescribed in connection with the block diagram embodiment of FIG. 15herein above.

In accordance with yet another aspect of the present invention, a LIDARsystem having an embodiment similar to the embodiment described inconnection with FIG. 15, for example, is operative to measure flowvelocity in three axes of a predetermined coordinate system as willbecome more evident from the following description. A suitableembodiment of the 3-axis flow velocity determination elements is shownin the block diagram schematic of FIG. 19. Reference numerals ofelements previously described for azimuth determination, scan positiondetermination, display and processing for the embodiment depicted by theblock diagram embodiment of FIG. 3 will remain the same for theembodiment of FIG. 19. Accordingly, these elements will operatestructurally and functionally the same or similar to that described forthe embodiment of FIG. 3 except that their use in the embodiment of FIG.19 will be for flow velocity measurement and display. Those elements ofthe block diagram of FIG. 19 not previously described will now bedescribed.

Referring to FIG. 19, as previously described for the LIDAR systemembodiment of FIG. 15, electrical return signals which are generated bythe light detector 314 in response to light reflections from a particlealong the predetermined scan pattern of the transmitted CW laser beamare passed over signal line 316 to the signal conditioning circuit 318which may comprise conventional amplification and filtering circuitsappropriate for conditioning the electrical signals. These electricalsignals will be burst signals of Doppler frequency content lasting aslong as a particle is within the width of the transmitted laser beamwhich will herein after be referred to as a “hit”. After the signalconditioning of the circuitry 318, each burst of electrical signaling issampled and digitized in an analog-to-digital (A/D) converter 440 inaccordance with a predetermined sampled data rate which may be on theorder of one-hundred and seventy-five million samples per second (175MSPS), for example. The resultant data samples of each hit are providedto a digital signal processor (DSP) 442 for processing to determine theDoppler frequency associated therewith which is stored in a memory 444thereof in the form of a data word for retrieval by the processor 88 aswill be more fully described herein below. The processing of thedigitized data samples of a burst or hit may take the form of a FastFourier Transform (FFT) algorithm or autocorrelator algorithm, forexample, programmed into the DSP 442. Signal lines 446 coupled betweenprocessor 88 and DSP 442 provide for handshaking and data word transfersas will become evident from the following description. In the presentembodiment, the processors 88 and 442 may be DSPs of the typemanufactured by Texas Instruments bearing model numbers TMS320-C33 andTMS320-C6201, respectively, for example. It is understood thatseparating out and performing the system functions in two digitalprocessors in the present embodiment offer design convenience and easeand that in an alternate embodiment, the functions of the DSP 442 may beprogrammed into a single DSP, like the processor 88, for example, whichmay perform by itself the functions of both processors 88 and 442. It isalso possible that more than two processors may be used to embody theoverall processing functions. Accordingly, this aspect of the presentinvention should not be limited to the number of processors, which willbe determined based on the particular application of the invention.

FIGS. 20 and 20A illustrate functionally the processing involved for thedetermination of flow velocity in the 3-axes of the predeterminedcoordinate system. As has been described herein above, in oneembodiment, the LIDAR system projects a laser beam 450 of apredetermined width in a conical pattern as shown in the illustration ofFIG. 20. In FIG. 20, a plane 452 which is circular in cross-section (seeFIG. 20A) is taken through the conical pattern at a range R from theLIDAR system where a hit 454 occurs. This plane or slice 452 is referredto herein as a scan circle brought about by the rotation of the opticalelement 52, for example. As described herein above in connection withthe embodiment of FIG. 3, each time the optical element 52 is rotatedpast a reference point of the cyclic rotation, a trigger signal isgenerated. This reference point is referred to as the trigger position456 of the scan circle. In the present embodiment, Y and Z quadratureaxes of the predetermined coordinate system exist in the plane of thescan circle. More particularly, the Y-axis is along a line 458 drawnfrom the center 460 of the scan circle to the trigger position 456 andthe Z-axis is along a line 462 drawn from the center 460 of the circle452 90° counter-clockwise from the Y-axis. The X-axis of the coordinatesystem is along a line 464 drawn perpendicular to the scan circle plane452 through the center 460 thereof. Accordingly, the X-axis is projectedfrom the apex of the conical pattern as it exits the LIDAR systemthrough the center 460 of the plane 452. Now that the ground-work hasbeen laid, the concept of determining the flow velocity in three axes,Vsx, Vsy, and Vsz, may be described.

Each time a hit like at point 454, for example, is detected from theresulting electrical signal burst, a Doppler frequency is determinedfrom the data samples of the associated burst. Knowing the wavelength ofthe laser beam, a one-axis flow velocity V1 for the hit may bedetermined from the corresponding Doppler frequency. In addition anangle a1 on the scan circle corresponding to the hit point 454 may bedetermined in relation to the Y-axis based on the elapsed time from thelast trigger signal and the scan circle period, i.e. the total time tocomplete a scan of the circle pattern, which will become more evidentfrom the description found herein below. The angle t that the hit makeswith the X-axis remains substantially fixed for the circular scanpattern. Accordingly, a set of three equations may be established forthree hits H1, H2 and H3 around the scan circle based on their singleaxis velocities V1, V2 and V3 and scan circle angles a1, a2 and a3(angle t being fixed for the present embodiment) using trigonometricidentities as shown by way of example in FIG. 20B. Referring to FIG.20B, the top, middle and bottom equations may be each solved for flowvelocities Vsx, Vsy and Vsz along the X-axis, Y-axis, and Z-axis,respectively. Also, knowing the azimuth position of the scan circlepattern from which the three hits are taken will establish a referencepoint in azimuth of the 3-axis flow velocity.

One complication arises by not knowing when a hit will occur, i.e. a hitmay not be forced to occur. Rather each hit occurs naturally as aparticle, such as dust or gaseous or vapor condensation, for example,crosses the width of the laser beam as it is guided along itspredetermined pattern. Another complication arises as a result of thelarge number of hits likely to occur and the burden on the processorshould all of the detected hits be processed. Thus, a selection criteriais desirable to determine which of the detected hits along the path ofthe scan pattern should be processed and which of the processed hitsshould be used to determine the 3-axis flow velocity. These selectioncriteria will be described in greater detail in the followingparagraphs.

In addition, the predetermined coordinate system described above fordetermining the 3-axis flow velocity is referenced to the LIDAR systemand may not be the same as the flight coordinate system of the aircrafton-board which LIDAR system is mounted. FIG. 21 exemplifies a LIDARsystem 470 mounted on-board an aircraft 472, which, for this example, isa helicopter, with the two coordinate systems of the LIDAR and aircraftbeing not the same. That is, the LIDAR scanner 470 has its X, Y and Zcoordinate system as described herein above and the aircraft 472 has itsown X, Y and Z coordinate system. Since it may be important that thepilot or operator know the flow velocity based on the aircraft'scoordinate system, the flow velocity of the LIDAR system Vsx, Vsy andVsz may be converted to a flow velocity referenced to the aircraft'scoordinate system Vax, Vay, and Vaz using a set of three equations shownby way of example in FIG. 21A. Transformation constants a_(ij) may beformed into a 3×3 matrix,, where i represents the column and jrepresents the row of the matrix. This 3×3 conversion matrix may operateon the LIDAR velocity vector which is expressed as a single columnmatrix comprising the velocity components of the LIDAR coordinate systemto obtain the aircraft's velocity vector which is also expressed as asingle column matrix comprising the velocity components of theaircraft's coordinate system.

An exemplary program flow organization for programming the processor 88to determine 3-axis flow velocity measurements is shown by the blockdiagram of FIG. 22. Referring to FIG. 22, upon turning on processor 88,a main program, which will described more fully in connection with theflow diagram of FIG. 23, is run to initialize the processor in block474. Next, the processor enters a foreground program in block 476 whichwill be more fully described in connection with the flow diagram of FIG.24. The foreground program 476 is executed continuously to call variousother programs like an evaluate function program 478 (see FIG. 28), avelocity function program 480 (see FIG. 29), and an output functionprogram 482 (see FIG. 30) based on a plurality of interrupt serviceroutines (ISRs), like a clock function ISR 484 (see FIG. 25), a triggerfunction ISR 486 (see FIG. 26), and a serial function ISR 488 (see FIG.27). In the present program organizational example, that which triggersthe clock function ISR 484 is a Timer 0 which may be a designatedregister of processor 88 configured to count through a total count whichrepresents a predetermined time period. Each time Timer 0 counts throughits predetermined time period, which may be 100 microseconds, forexample, the function clock ISR 484 is executed. Another register ofprocessor 88 may be designated as Timer 1 and configured to startcounting from zero each time the processor 88 receives the triggersignal 116 described in connection with the embodiment of FIG. 19through a an interrupt port INT 0. The trigger signal 116 causes thetrigger function ISR 486 to execute. Also, when a data word is receivedfrom DSP 442 via a serial Port 0, it will be stored in a register of theprocessor 88 designated as a data receive register 490 as will be morefully described below. Upon completion of the transfer of the data wordinto processor 88, the serial function ISR 488 is executed.

Referring to FIG. 23 which includes an exemplary software flow diagramof the main program 474, in block 492, the serial Port 0 is configuredto be the port through which requests for data words are made to the DSP442 in response to the generation of a Frame Sync Signal 494 by theforeground function routine 476 (see FIG. 22). Port 0 is also configuredby block 492 to receive the data word from the DSP 442 and store it intoregister 490 and call serial function ISR 488 upon completion of thedata word transfer. In block 496, Timer 0 is configured to call theclock function ISR 484 each time it counts through a countrepresentative of 100 microseconds, for example. In block 498, Timer 1is configured to count freely until reset by the trigger function ISR486. In block 500, the INT 0 port is configured to call the triggerfunction ISR 486 each time a trigger signal 116 is received over a linecoupled thereto from the scan pattern scanner 52 (see FIG. 19). In block502, a display write function of processor 88 is initialized withcertain commands well-known to all those skilled in the pertinent art toform text messages and control the screen of the display 154. Once theinitialization tasks of the main program 474 are complete, theforeground function routine 476 is called by block 504.

Referring to FIG. 24, in block 506, it is determined whether or not a“Get Data Flag” 508 is set true which is effected every 100 microsecondsby the clock function ISR 484. If true, block 510 generates the FrameSync Signal 494 to Port 0 to initiate the request for a data word fromthe DSP 442, sets the Get Data Flag 508 false, and executes decisionalblock 512. If the Get Data Flag 508 is determined to be false by block506, the execution of block 510 is bypassed and decisional block 512 isexecuted. In block 512, it is determined whether or not a Data ReadyFlag 514 is set true by the serial function ISR in response to thecompletion of the transfer of the data word into register 490. If true,the evaluate function routine 478 is called for execution by block 516.Upon completion of the tasks of the evaluate function 478, programexecution is returned to 516 whereupon the Data Ready Flag 514 is setfalse and block 518 is executed. If the Data Ready Flag 514 isdetermined to be false by block 512, then block 516 is bypassed anddecisional block 518 is executed. In block 518, it is determined whetheror not a Display Flag 520 is set true by the clock function ISR 484. Iftrue, block 522 calls the velocity function routine 480 for executionand when its tasks are complete, program execution is returned to block522. Block 522 next calls the output function routine 482 for executionand when its tasks are complete, program execution returns to block 522which next sets the Display Flag 520 false. Upon completion of theexecution of block 522 or if the Display Flag 520 is determined to befalse by block 518, program execution is returned to decisional block506 and the program flow repeated. In this manner, the foregroundfunction 476 is continuously executed.

Referring to the flow diagram of FIG. 25, each time the Timer 0 countsthrough its predetermined count, i.e. every 100 microseconds, programexecution is interrupted and the clock function ISR 484 is called forexecution. In block 526, the Get Data Flag is set true and a Displaycounter which may be a designated register of the processor 88 isincremented by one count. Next, in block 528, it is determined whetheror not the count of the Display counter has reached a desired countwhich is indicative of an increment of time. For example, if the Displaycounter is incremented one count every 100 microseconds and theincrement of time desired is 250 milliseconds, then the desired countwould be 2500. Accordingly, the Display counter is a vehicle used toestablish time increments of 250 milliseconds in the present embodiment.Thus, every 250 milliseconds as determined by block 528, block 530 setsthe Display Flag true and resets the Display counter to zero.Thereafter, program execution returns to where it was interrupted andthe clock function ISR 484 sits idle waiting for the next internalinterrupt from Timer 0.

Referring to the flow diagram of FIG. 26, each time the trigger signal116 is received by the interrupt port INT 0, program execution isinterrupted and the trigger function ISR 486 is called for execution. Inblock 532, the count in Timer 1 which is representative of a period ofone scan cycle is read and stored in a designated register of processor88 and Timer 1 is reset to zero count. Thereafter, program executioncontinues from its interruption point and the trigger function ISR sitsidle waiting for the next external interrupt signal 116. Referring tothe flow diagram of FIG. 27, each time the data word transfer iscompleted, the serial function ISR 488 is called for execution. In block534, the data word of register 490 which is indicative of the Dopplerfrequency of the hit and the count of Timer 1 which is indicative of thecorresponding scan circle angle a1 of the hit are read and stored indesignated registers of the processor 88 and the Data Ready Flag is settrue. Thereafter, program execution continues from its interruptionpoint and the serial function ISR sits idle waiting for reception of thenext internal interrupt signal.

In accordance with the foregoing described embodiment, the processor 88requests and inputs a data word from the DSP 442 every 100 microseconds.Since it is unknown whether or not a hit has occurred during the mostrecent 100 microsecond interval, it is not known if the received dataword from the DSP 442 for the current 100 microsecond interval is thesame data word received for the previous 100 microsecond interval, i.e.no hit during the current interval. Thus, some indication should beprovided to the processor 88 to indicate that at least one hit occurredduring the current interval. In the present embodiment, this indicationis provided in the form of one of the bits of the data word designatedas “New Bit” being set to a “1” to indicate that the data word isrepresentative of the Doppler frequency of a hit during the currentinterval. Accordingly, with each received data word from the DSP 442, anevaluation thereof is performed by the evaluate function 478, a flowdiagram of which being shown in FIG. 28.

Referring to the flow diagram of FIG. 28, in block 540, it is determinedwhether or not New Bit is set to a “1” in the received data word. Ifnot, program execution of the evaluate function routine 478 is abortedand execution is returned to block 516 of the foreground routine 476.Otherwise, it is next determined in block 542 if the new data word isthe first hit or data point for the current evaluation period. If so, inblock 544, the data word (Doppler frequency) and angular position of thefirst hit or data point is stored and designated as belonging to thefirst data point. Also, in block 544, and target positions for the 2ndand 3rd hits along with acceptance regions therefor are established. Inthe present embodiment, the target positions for the 2nd and 3rd hitsmay be approximately 120° and 240°, respectively, in relation to theposition of the first data point and the acceptance regions of each maybe on the order of ±60°, for example. Then, in block 546, a data pointcounter of processor 88 having a count indicative of the number of datapoints received for the present evaluation period is incremented by one.Program execution is then returned to block 516.

If, in block 542, it is determined that the most recent data point isnot the first, then, in block 548, its angular position is determinedfrom a ratio of the count of Timer 1 corresponding to the recent hit andthe count representative of the period of the scan cycle. The angularposition of a data point subsequent the first data point is subtractedfrom the angular position of the first data point. Next, in block 550,it is determined if the difference in angular position is within thetarget and acceptance region for the 2nd data point or 120°±60°, forexample. If so, in block 552, the data word (Doppler frequency) and itscorresponding angular position are stored and designated as belonging tothe 2nd data point. Also, in block 552, after each 2nd data point withan acceptable target and acceptance region is determined, the acceptanceregion is tightened. For example, after the first 2nd data point, theacceptance region may be set to ±50°, and after the second 2nd datapoint, the acceptance region may be set to ±40°, and so on until no more2nd data points fall within the region. This evaluation process ensuresthat only the closest 2nd data point to the target of 120°, for example,will be used in the determination of the 3-axis flow velocity. Further,in block 552, a “Point 2 Valid Flag” is set true to indicate that a 2nddata point is found valid for processing. If it is determined that asubsequent data point to the first data point is found not to be withinthe target and acceptable regions set for the 2nd data point, then inblocks 554 and 556, the same processing as for blocks 550 and 552 isrepeated for the 3rd data points to establish a 3rd data point withinthe closest acceptable region of the set target angle or 240°, forexample, in relation to the first data point. After each execution ofeither block 552 or block 556, the data points counter is incremented byone in block 546 so that its total count is representative of the totalnumber of data points evaluated for the current evaluation period whichmay be on the order of 250 msec., for example. In this manner, threedata points are selected from all of the data points processed in each250 msec. period and their respective angular positions are the closestto being 120° apart along the scan circle pattern.

An example flow diagram of the velocity function routine 480 which isrun every 250 msec. in the present embodiment is shown in FIG. 29.Referring to FIG. 29, in block 560, the data point counter is read todetermine if at least three data points were processed in the precedingevaluation period. If so, in block 562, it is determined if the ValidFlags for the 2nd and 3rd data points are set true which is anindication that there are three data points which fall within thepredetermined acceptance criteria of relative angular positions aboutthe scan circle, i.e. the selected data points. If so, then three singleaxis velocities V1, V2 and V3 are determined in block 564 from theDoppler frequencies (data words) of the selected three data points.Thereafter, in block 566, a 3-axis flow velocity measurement isdetermined from the three single axis velocities V1, V2 and V3 and theirrespective angular positions a1, a2 and a3 (t being fixed for all 3 datapoints) in accordance with the exemplary equations of FIG. 20B, forexample. The velocity components Vsx, Vsy and Vsz based on thepredetermined coordinate system of the LIDAR may be converted tovelocity components Vax, Vay and Vaz of the aircraft on-board which theLIDAR system is mounted in block 568. And, in block 570 the data used inthe aforementioned calculations may be characterized in some manner. Forexample, a data validity flag may be set to good data, if the data pointdistribution in the acceptance regions is considered good, and a datarate may be calculated. Finally before returning execution to block 522of the foreground function routine, all of the flags set by the evaluatefunction routine 478 in the previous evaluation period are reset inblock 572 for the next evaluation period.

Now, if it is determined in block 560 that in the previous evaluationperiod less than three data points were processed, then, the dataquality will be characterized by setting data validity to a low datarate, for example, and calculating the data rate in block 574. Also, ifit is determined in block 562 that there are not three valid data pointsfor processing based on the current acceptance criteria for data pointdistribution, then, in block 576, the data may be characterized bysetting data validity to poor data distribution, for example, andcalculating the data rate. After either block 574 or 576, programexecution is passed to block 572 for resetting the flags as previouslydescribed.

An exemplary flow diagram of an output function routine 482 suitable foruse in describing the programmed processing of the processor 88 is shownin FIG. 30. This routine 482 is also called every 250 msec., forexample, after the velocity function routine 480 is executed. Referringto FIG. 30, in block 480, it is determined if data validity was set atlow data rate and if so, certain message text is selected for display onthe screen of the display 154 in block 582. For example, a text messagewhich displays an indication of Low Data Rate may be generated and sentto the display by blocks 582 and 588. Also, a signal which is formattedto indicate low data rate may be generated and provided to an interfaceto other aircraft avionics by blocks 582 and 588. Similarly, if it isdetermined in block 584 that data validity was set to poor datadistribution, then an appropriate text message may be generated and sentto the display and formatted for distribution to other aircraft avionicsto indicate this condition by blocks 586 and 588. If neither block 580nor block 584 determine a true or affirmative condition, blocks 587 and588 generate and send a text output or message indicative of the 3-axisflow velocity measurement to the display screen, and also, format thevelocity measurement and send it to other aircraft avionics over signalline(s) interfaced with the processor 88, for example. After block 588completes its tasks, program execution is returned to block 522 of theforeground function routine 476.

While an embodiment of a combined LOAS and LIDAR system has beendescribed herein above in connection with the block diagram of FIG. 15,it is understood that from a practical perspective when applied to amoving vehicle like a helicopter or UAV, for example, the common opticalelements 284 may be embodied in a scan head 600 remotely located fromthe optical elements of a single LOAS 280 or the combined LOAS 280 andLIDAR system 282 such as shown in the exemplary block diagram schematicof FIG. 31. Common elements between the embodiments of FIGS. 15 and 31will have like reference numerals. In the embodiment of FIG. 31, theoptical elements of 280 and 282 may be disposed within the vehicle andwell supported and protected from the environment of the vehicle.Conventional fiber optic cabling, like that shown in isometric view inFIG. 37 and cross-sectional view in FIG. 37A. for example, may be usedfor the optical paths 18 and 319 leading to and aligned with thedichroic filter optical element 320 which was previously described forthe embodiment of FIG. 15. A further fiber optic cable (see FIGS. 37 and37A) provides for the optical path 322 from the dichroic filter 320 tothe scan head 600 which includes the common optical elements 284. Thefiber optic cabling for the optical path 322 may take a circuitous routewithin the vehicle to reach the scan head 600 which may be mounted tothe external surface of the vehicle to permit the beam scan patterns tobe projected out from the vehicle. More than one scan head may be usedin the present embodiment as will become more evident from thedescription found herein below.

A suitable embodiment of the scan head 600 is shown in the sketch ofFIG. 32. This scan head controls movement of the optical beam scanpatterns along three axes 602, 604 and 606. A top 608 of the scan head600 may be mounted to a surface of the vehicle, like the frontunderbelly of a helicopter or UAV, for example, such as shown in thesketch of FIG. 21. A window area 610 of the scan head 600 through whichthe beam scans are emitted would be pointed in the direction of movementof the vehicle or flight path, if the vehicle is an aircraft. The fiberoptic cable of the optical path 322 may be passed through a hole in theskin of the vehicle and into the scan head 600 through an opening 612 atthe top 608 thereof. The optical elements within the scan head 600 whichwill be described in greater detail herein below cause the beams passedby the path 322 to be scanned 360° about the axis 606. A conventionalmotor assembly (not shown) within the scan head 600 controls movement ofa lower portion 614 thereof ±90° about the axis 602 azimuthally withrespect to the flight path of the vehicle. This movement occurs along aseam 616 between the top and bottom portions, 608 and 614, respectively,and effectively moves the axis 606 along with the lower portion 614which projects the beam scan pattern through a helical pattern much thesame as that described in connection with the example of FIG. 2.

Another portion 618 of the scan head 600 which includes the window area610 and falls within the portion 614 moves azimuthally with the portion614. Another conventional motor (not shown) disposed within the scanhead 600 controls movement of the portion 618 about the axis 604 +30° to−90° in elevation, for example, with respect to the flight path ordirection of the vehicle. This movement causes the axis 606 and scanpatterns to move in elevation with the portion 618. In the presentembodiment, the window area 610 of the portion 618 may be controlled tomove upward and inside the portion 614 to protect it from theenvironment when not in use. The corrugated skin or surface in the area620 at the top portion 608 acts as a heat sink to improve the transferof heat away from the scan head 600 during operation thereof.

A sketch exemplifying the common optical elements inside the scan head600 is shown in FIG. 33. Referring to FIG. 33, the fiber optic cablingof the optical path 322 is aligned with the axis of the input apertureof the beam expander 20. The beam exiting the expander 20 may bereflected from a fold mirror 325 over an optical path 324 and passedinto the rotating optical element 32. In the present embodiment, therotating optical element 32 comprises a rotating optical wedge element622 centered and rotated about the axis 606 and having a flat surface624 at its input side and a surface inclined at a predetermined angle atits output side. It is understood that other elements may be used forthe rotating optical element 32, like a transparent liquid crystalscanner, for example, without deviating from the broad principles of thepresent invention.

The beam conducted over path 324 is aligned with the axis 606 and passedfrom the input side to the output side of the wedge element 622. Thelight beam is refracted in its path through the wedge element 622 andexits perpendicular to the inclined output surface 626 thereof. Thisrefraction of the light beam causes it to exit the scan head 600 as beam36 through the window area 610 at an angle 628 to the axis 606.Accordingly, as the wedge optical element 622 is rotated 360° about theaxis 606, the beam 36 is projected conically from the scan head 600 toform the scan pattern 630. Return beams will follow the same opticalpaths as their emitted beams as described herein above. The window area610 may comprise a clear, flat, zero power optical element made of amaterial like glass, for example, so as not to interfere substantiallywith the scan pattern of the exiting beam 36. In the present embodiment,the wedge optical element 622 and window 610 are structurally coupled tomove together along the azimuth path 632 and elevation path 634 to causethe optical axis 606 to move along therewith. In this manner, the scanpattern 630 is forced to move in azimuth and elevation with the portions614 and 618 of the scan head 600.

As noted above, the present invention may be embodied to include morethan one scan head mounted at different locations on the vehicle.Depending on the application, some of the scan heads may utilize feweroptical elements and less scan angle than that described for theembodiment of FIGS. 32 and 33. In one application, the scan head 600 maybe mounted at the front under belly of a helicopter or UAV as describedherein above to detect objects and wind conditions at the front andsides of the aircraft, for example, and a second scan head 640 may bemounted at the tail section of the helicopter, for example, to detectobjects at the rear and sides of the aircraft. A system suitable forembodying this application is shown in the block diagram schematic ofFIG. 34. In this embodiment, an optical switch 642 is disposed in theoutput optical path 644 of the LOAS 280. The path 644 may be formed by afiber optic cable (see FIGS. 37 and 37A). The optical switch 642 may becontrolled by a signal 646 to direct the beam of path 644 to one of aplurality of optical paths. For example, the optical switch 642 may becontrolled to direct the LOAS beam over the fiber optic cable of path 18to the dichroic filter 320 and on to the scan head 600 as describedherein above in connection with FIG. 31, or to direct the beam over anoptical path 648, which may be formed by a fiber optic cable (see FIGS.37 and 37A), to the tail scan head 640, or to direct the beam to otherscan heads (not shown) mounted elsewhere on the vehicle over otheroptical paths 650. The return beam will follow substantially the sameoptical path as the directed beam.

A suitable embodiment of the high-speed optical switch 642 is shown inthe sketch of FIG. 35. In this embodiment, a flip mirrored element 652is mounted with vertical hinges 654 and 656 to be controlled in ahorizontal rotation thereabout and is mounted with horizontal hinges 658and 660 to be controlled in a vertical rotation thereabout. The opticalswitch may be fabricated on a substrate using micro-electromechanicalsystem (MEMS) techniques with miniature motors coupled to the hingedmountings for controlling the movement of the mirrored element 652 todirect the beam 644 to one of the optical paths 18, 648, or 650 at anygiven time. Accordingly, the beam 644 and its returns may be multiplexedamong the aforementioned paths by controlling the optical switch withthe control signal 646 which positions the motors of the switch. It isunderstood that the embodiment of FIG. 35 is merely an exemplaryembodiment of the optical switch 642 and that other embodiments may beused just as well. For example, a rotating disc having a portion that issubstantially clear to permit passage of the beam and its returns alongone of the paths 18, 648 or 650, and a portion that has a reflectivecoating to cause the beam and its returns to be reflected along anotherof such paths may be positioned by a motor controlled by the controlsignal 646 to direct the beam 644 and its returns to a designatedoptical path by passage or reflection thereof.

In yet another embodiment as shown by the block diagram schematic ofFIG. 36, multiple scan heads may be mounted at various locations on thevehicle to detect objects and determine wind conditions at predeterminedregions surrounding the scan head locations. For example, one scan head662 may be located at one wing of an aircraft or side of a vehicle andanother scan head 664 located at the other wing or side. The scan head662 which may be mounted on the right wing or side with respect to thedirection vector of the vehicle may be adjusted to scan azimuthally from0° to +90° (0° being the direction vector of the vehicle) to cover thefront right side region of the vehicle. Similarly, the scan head 664which may be mounted on the left wing or side with respect to thedirection vector of the vehicle may be adjusted to scan azimuthally from0° to −90° to cover the front left side region of the vehicle. Otherscan heads may be mounted at other locations like at the tail of theaircraft or rear of the vehicle, for example. All such scan heads areprocessed by a single LOAS or a combined LOAS 280 and LIDAR 282 system.For this reason, a high speed optical switch 666 is utilized andcontrolled to multiplex the emitted beams of the single or combinedsystem and their returns among optical paths 668, 670 and 672 to andfrom the scan heads 662, 664 and others, respectively. In the presentembodiment, the switch 666 may be disposed in line with the optical pathof the LOAS and/or LIDAR beams exiting the dichroic filter 320 and maybe the same or similar to the type of optical switch used for theembodiment of FIG. 35 described herein above.

While the aspects of the present invention have been described hereinabove in connection with a variety of embodiments, it is understood thatthese embodiments were merely provided by way of example and should notbe considered limiting to the present invention in any way, shape orform. Rather, the present invention and all of the inventive aspectsthereof should be construed in accordance with the recitation of theappended claims hereto.

What is claimed is:
 1. A wide field scanning laser obstacle awarenesssystem (LOAS) for use on-board an aircraft for alerting an operator ofobstacles posing a risk of collision with said aircraft, said systemcomprising: a light source for generating a pulsed laser beam of light,a light detector; a plurality of optical elements for directing saidpulsed laser beam from said system with a predetermined pattern scannedazimuthally over a wide field, said plurality of optical elements alsofor receiving reflections of said pulsed laser beam from at least oneobject along said predetermined pattern and directing said laser beamreflections to said light detector; wherein the predetermined patternincludes a variation in elevation of the directed pulsed laser beam inrelation to an elevation of the aircraft; means for determiningsubstantially the azimuth position of the directed pulsed laser beam;means for determining substantially the elevation of the directed pulsedlaser beam; display apparatus including an image screen for displaying alimited field of view, wherein the wide field of view of the systemextends substantially beyond the field of view of the image screen;processor means coupled to said light detector, display apparatus,azimuth position determining means and elevation determining means fordetermining the location of the at least one object in range, azimuthand elevation in relation to a flight path of the aircraft, saidprocessor means for driving said display apparatus to display anindication representing the at least one object in range, azimuth andelevation; and wherein the indication of the at least one objectcomprises an image of a bar, said bar image disposed vertically at thefar left of the screen of the display apparatus when the object locationis azimuthally outside the field of view of the display apparatus to theleft, and said bar image disposed vertically at the far right of thescreen of the display apparatus when the object location is azimuthallyoutside the field of view of the display apparatus to the right.
 2. Thesystem of claim 1 wherein the display apparatus comprises amulti-functional display.
 3. The system of claim 1 wherein theindication of the at least one object is overlayed with an existingimage on the screen of the display apparatus.
 4. The system of claim 1wherein the bar image is controlled to change color and height based onthe risk of collision with the aircraft posed by the object representedthereby.
 5. The system of claim 4 wherein the bar image is controlled tochange color based on the range of the object to the aircraft inrelation to the flight path thereof.
 6. The system of claim 4 whereinthe bar image is controlled to change height based on the relativeheight of the object in relation to the elevation of the aircraft.
 7. Ascanning laser obstacle awareness system (LOAS) comprising: a lightsource for generating a pulsed laser beam of light, a light detector; ascan head remotely located from said light source and light detector; atleast one first optical element configured to direct said generatedpulsed laser beam over a first fiber optic cable to said remote scanhead; said scan head including at least one second optical element fordirecting said pulsed laser beam from said scan head with apredetermined scan pattern, said at least one second optical elementalso for receiving reflections of said pulsed laser beam from at leastone object along said predetermined scan pattern and directing saidlaser beam reflections to a second fiber optic cable over which saidlaser beam reflections are returned to said remote light detector foruse in determining the location of said at least one object.
 8. Thesystem of claim 7 wherein the at least one second optical element beingrotated in azimuth by the scan head to scan the predetermined scanpattern over an azimuth field.
 9. The system of claim 7 wherein the atleast one second optical element being rotated in elevation by the scanhead to scan the predetermined scan pattern over an elevation field. 10.The system of claim 7 including a plurality of scan heads remotelylocated from the light source and light detector; wherein light iscoupled selectively between the at least one first optical element andthe plurality of scan heads along a corresponding plurality of firstfiber optic cables.
 11. The system of claim 10 wherein the at least onefirst optical element includes an optical switch controllable to couplelight between the light source and a selected scan head of saidplurality along a corresponding first fiber optic cable.
 12. The systemof claim 11 wherein the optical switch comprises a flip mirror operatedto rotate about at least one axis.
 13. The system of claim 11 whereinthe optical switch is fabricated using MEMS techniques.
 14. The systemof claim 10 wherein each scan head of said plurality for receivingreflections of the pulsed laser beam scanned thereby and for directingsaid laser beam reflections along a corresponding second fiber opticcable to the remote light detector, wherein said laser beam reflectionsare received by each scan head of the plurality and returned to saidremote light detector over the second fiber optic cable correspondingthereto.
 15. The system of claim 10 wherein the LOAS is disposedon-board an aircraft; wherein the light source, the light detector andat least one first optical element are disposed at a first location ofthe aircraft and the plurality of scan heads are distributed at acorresponding plurality of second locations along the surface of theaircraft remote from said first location; and wherein each scan head fordirecting light therefrom at the predetermined scan pattern of the atleast one optical element thereof.
 16. The system of claim 7 wherein theat least one second optical element includes a laser beam expander forexpanding the pulsed laser beam prior to being directed from the scanhead with the predetermined pattern.
 17. The system of claim 16 whereinthe laser beam expander is configured in the scan head to receive anddirect the laser beam reflections to the second fiber optic cable. 18.The system of claim 7 wherein the first and second fiber optic cablesare part of a common fiber optic cable.
 19. A wide field scanning laserobstacle awareness system (LOAS) for use on-board an aircraft foralerting an operator of obstacles posing a risk of collision with saidaircraft, said system comprising: a light source for generating a pulsedlaser beam of light, a light detector; a plurality of optical elementsfor directing said pulsed laser beam from said system with apredetermined pattern scanned azimuthally over a wide field, saidplurality of optical elements also for receiving reflections of saidpulsed laser beam from at least one object along said predeterminedpattern and directing said laser beam reflections to said lightdetector; wherein the predetermined pattern includes a variation inelevation of the directed pulsed laser beam in relation to an elevationof the aircraft; means for determining substantially the azimuthposition of the directed pulsed laser beam; means for determiningsubstantially the elevation of the directed pulsed laser beam; displayapparatus comprising a panel of at least one row and at least one columnof light indicators; and processor means coupled to said light detector,display apparatus, azimuth position determining means and elevationdetermining means for determining the location of the at least oneobject in range, azimuth and elevation in relation to a flight path ofthe aircraft, said processor means for driving said light indicators ofthe display apparatus to represent a location of the at least one objectin azimuth and elevation.
 20. The system of claim 19 wherein the lightindicators are controlled to change color to indicate the risk ofcollision of the at least one object with the aircraft.
 21. The systemof claim 19 wherein the light indicators are controlled to change colorto indicate the range of the at least one object to the aircraft. 22.The system of claim 19 wherein the light indicators comprise diodesoperative to emit light of different colors.